question of is it allowed to archive geometry dash projects that got deleted by RobTop game creator

If you have a remix of such a project I would not recommend you post it.

You may save personal copies of projects in case they get taken down(Hell, I've done that with Sprunki projects!), but keep them to yourself.

Posting copies can get you in trouble with the Scratch Team, or in your case, RobTopGames.

It depends. There's nothing wrong with having an unshared gd project that was a remix of one of the projects taken down, but if you share it and don't give credit, then it will probably be taken down, especially if you've had another gd project taken down already. Even though many people thought that RobTop taking down games on a kids coding site, but it actually started when other gd sites started stealing gd levels from @iPhone_ATT_TWC115 and putting them on their sites. This actually caused competition between the fake and real gd sites, so robtop had to take down the scratch games.

Hehehehehehehe