I am impressed with DnD Beyond but am concerned that if i invest in digital resources they will disappear in time if for example a 6tth edition appears

if for example i buy the players handbook will it upgrade to a new edition when that happens?  Also what will happen if i only buy parts of the book?  
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It also worries me that i couldn't find an answer to this question in the FAQs when i'm sure its one that everyone has asked

There's been no official comment, but I can't imagine you'd get the 6th edition material for free. Each version has been treated like a new game. It'll be new books, new adventures, different mechanics, etc.

On a positive note, there's been no hint that 5th edition has slowed down at all. D&D has never been more popular within gaming communities, and has never been more prevalent in pop culture. There's a long thread on speculation of when 6th edition is releasing. Short answer is you'll be good for quite some time, as there have been no hints of 6th edition being tested or written. Even then, you can still find people playing 3.5e. Even when 6e comes out, there's nothing saying you absolutely must switch to the new system. 5e is very easy to pick up, and will be popular for many more years.

I also don't think 5th edition will disappear from this site, they might stop to add new additions but they probably keep the access to the content and character creation for 5e, at least for some years. They might have offers to upgrade to 6e, but for sure not 6e content for free.

Anyway, there are more chances of having a revision of 5e than having a 6e, in that case the material here would get updated.

If that happens, we're talking years and years down the line. D&D Beyond is an online 5th edition resource, and WoTC has committed to supporting 5e (their most popular edition ever) for the foreseeable future. 

They also said that the next edition (whenever it comes) would be backwards compatible with 5e.

Considering people are still buying and played 3.5 edition, there is no reason why D&D Beyond would delete all the 5e stuff. If they wanted to offer 6th edition stuff they can just do that as an addition - so users could just select "6th Edition Character Builder" if necessary and so on. If D&D Beyond just outright deleted all the 5th edition stuff they had - they'd be finished as a business. Hundreds of thousands of people (they have over 4 million members) will get very angry, stop using the site, make this publically known, and hinder all future sales driving people to the companies that didn't screw over the customers. D&D Beyond aren't that stupid. So, you can be assured they'd just offer 6th edition as well as 5th edition. They probably won't host the stuff forever, but even after 6th edition releases they'd likely still host 5th stuff for several years. Not only to avoid the back-lash but also because it will be profitable to do so - people will still be buying 5th edition stuff for years even then. Just like they're still buying 3.5 (and even 4th, let's not judge) even today.

Does DDB pay WOTC for each sale of PHB?  I assumed so?  If so then you would need to buy the new book.  

Quote from GregCa >>

Does DDB pay WOTC for each sale of PHB?  I assumed so?  

 Yes.

I got a feeling 5e is going to be it. Like windows 10 is supposed to be Microsoft's final iteration. And they just keep refining the build. I think that's what's going to be going on with 5e. I'm sure eventually it will change enough to get a 6e, but I don't even think we're close to 5e's half life yet. It wouldn't surprise me if we got a good 10 more years from it. We're already about to be 6 years in, and not even at at 5.5e stage yet.

There are not plans for 6th edition anytime soon. 5th edition is still going strong.

I would imagine that the content would not upgrade, but would still be available.

I can't imagine the 5e content going away - a new edition of DnD doesn't make the previous editions obsolete. I do expect that it will be moved into a legacy or bookshelf tab that allows you to access/buy content, but clearly places a new edition front and center. (ooo, brainstorm... a bookshelf view of the content you've bought on DDB... spines and covers and a shelf...)

While I would absolutely love to be wrong, I also don't foresee any free 'upgrades' to a 6e, 5.5e, etc. Even if it's a .5 update like 3.5e, it's essentially a new set of core books.

Given the talk of a complete overhaul in the way races are created, 6th edition may not be as far away as you might think.

I don't think changing the creation of races justifies a whole new edition. It has to be a bigger change than moving stats to background and changing descriptions. This would justify a 5.5e though, just as it happened with 3.5e.

A new edition needs more than updates on races or classes, it'd need to change the core mechanics.

I think we're far more likely to see another big book like Xanathar's than a 5.5e or a 6e.

D&D Beyond staff please answer OP

They may not know.  They are a licensee to 5e.  They don't have a license for prior editions, and I suspect they don't have an indefinite license that would include a hypothetical future edition.  Nor do they know WotC production schedule, or at least aren't in position to comment on it publicly.

Given how difficult it has been for them to implement 5e into DDB, to the extent that it still is not fully done, I find it laughable to think they're going to be able to somehow have 2 editions living together on the same site. I would be shocked if DDB could actually make it work that both 5e and 6e can coexist here without taking so many years to do it that 7e is already out.

I repeat, D&D Beyond staff please answer OP

I don't care if they get 6th edition, but I want to know that everything I've already purchased won't just disappear. at least with a physical copy, I know it won't be revoked because a new product comes out, with digital services it isn't so clear. even amazon can delete your purchased library if they feel like it, with no refunds or compensation. 

Everything you purchased will, eventually, disappear. At some point. The question isn't if, but when. If it's in 2030, maybe you don't care. If it's in 2023, you very well might.

Quote from vallhundfadewalker >>

I repeat, D&D Beyond staff please answer OP

 Calm down, man. They don't have some secret master plan to turn off their own income stream and screw you over. They don't know if/when a 6e will be revealed any more than we do. If you really want to speak directly to them, this is not the forum for it.

This is the reality of digital resources. You never lose the content you buy because you can download the pdfs, but the services provided here may not last forever.

WotC did maintain the 4e online character builder for several years after 5e came out, but it ran on an outdated platform and eventually died out. The web-based DDB platform is considerably more futureproof though and I'd expect it to stay up well into the future as long as DDB retains its license and remains solvent.