Uneven table numbers

I had the same situation, had all tables planned and also a mirror with the seating chart and a few guests cancelled few hours before the wedding, so before the meal I just moved people around, told them which table to sit and everyone was quite happy 😊

If you know who is not coming and are not able to backfill their places maybe let the venue know and ask them to move people around so the tables dont look empty, you may be able to remove a whole table so you have more full than a few half full if that makes sense. you can then let the moved guests know that whilst the table plan has them on Table A they will noe be on Table B etc. As long as you have name place settings they will find their seat.