Are these sentences correct:

[color=red]1-They should have left the building, as you should have.
[color=indigo]2-They should have left the building, as should have you.


Both sentences are technically correct but both sound very awkward. The second sentence in particular sounds horrible. I suggest a better way of expressing the same idea would be: They should have left the building and so should you.

Surely this is changing the tense…
the original is saying “you should have left when they should have left [in the past]”,
while your sentence is saying “they should have left, and you should leave now.”

I agree that it’s an awkward thing to express, and I don’t like 2 at all, but 1 seems just about ok.

I think it’s the ‘as’ that is awkward, so perhaps, “They should have left the building, and you should have left too.”

This isn’t a change of tense because in my suggestion ‘have left’ is understood.