But if the average compliment of the 39 starships was say about 400 then that means a fair number of people survived the destruction of their particular starship and any assimilation that took place.Gertting back to numbers, 11,000 people "lost" (dead/assimilated/still missing after all those years) would mean about 275-300 per ship in the low-end estimate of ship numbers
From the time of the battle, until the Enterprise arrived was something like two or three hours, plenty of time for crews to abandon the useless hulks of their starship and leave the area.
Why stay?
Or the rather large life boat possessed a warp drive.Since Sisko's escape pod was not found by USS Enterprise, someone had to have picked them up.