RBR - yes, the 3% is required. The real question is whether you want to revert to ADP/ACP testing or not, and whether to preserve the top heavy exemption. Since due to an asset sale, you have the option to pay the required 3%, and preserve the safe harbor status for the short year, preserve the top heavy exemption, and avoid ADP/ACP testing. (I'm assuming no other contributions that would otherwise invalidate the top heavy exemption anyway.)
If you don't choose this option, then you still have to pay the 3% for the short year, but you must test for ADP/ACP, and you lose your top heavy exemption since now it isn't a safe harbor plan.