l like the dragon mask items (and the mask of the dragon queen) and l have been thinking of ways to implement them (dragon hord loot/on a dragon worshiper like in skyrim) but l was woundering lf l had to be running that storyline to add them. (though l expect the answer will be "you are the dm so you can do whatever you want") but lf l do add them,l am worryed that the players might think l have plans to add that story to the campain (which l might not) which would dissapoint them or something.

You are the DM, so you can do whatever you want.

Seriously though, I wouldn't worry about it. They are powerful items though, so use sparingly.

As DxJxC said, and as you expected, it's up to you as the DM.

In my game the DM let me use one despite it being a game Tiamat doesn't exist in. It was just reflavoured that the mask was a creation by a dragon as a gift to my character for saving its life from evil cultists.

I cannot emphasize this enough, don't give too many magic items to the party. It will ruin your game, I know from experience. If you give too many magic items (especially very rare and legendary) to your party at lower levels, you as a DM will not have a good time.

But yeah, I would definitely use the Dragon Masks in a homebrew campaign. I was thinking about having them appear in my Descent into Avernus campaign.