Which is akin to 'an anti-magic field suddenly pops up'.
A good DM would have anticipated the use of Wish in such a way, created a backstory that 'the person who placed the skull in the tomb Wished that it could only be removed via X, Y and Z', or 'placed it in a demi-plane warned by a dimensional lock spell, and factored in a Legend Lore to discern the PCs learning this info in the first place.
If you ever find yourself as DM back peddling and trying to come up with contrivances to force the PCs on your plot after the fact (i.e. they were not present in the adventure as designed) it's a good indication you lack the epxerience of running high level games.
Im almost of the view you need to run a game to 20th, and watch as your players ruin your encounters to get a handle on how high level play handles, in order to become a good DM of high level PCs.