Board Game Arena

After a revolution, the power of the cards is reversed - 3 is highest, etc. If playing with Illegal Finish does going out with a 3 become an Illegal Finish?

Yes, the option description which can be seen in the rule set text also says so.

There are warnings when you are about to do an illegal finish usually.
However, if you have a 3 and 4 other cards, and perform a Revolution with, it does not warn you that your 3 will be an illegal finish.

A warning would be nice given how it usually warns you otherwise.