If she drops out the Democrats need to force everyone out and endorse Warnock.
No, they need to force Warnock to drop out and endorse Lieberman (i.e. the strongest - or rather, least weak - Democrat running). Of course, they should be spending on the regular Georgia Senate race since unlike Warnock or Lieberman, Osoff actually has a chance of winning even if it's a long shot and the money would be much better spent on Maine, North Carolina, Montana, and (if Kobach is the Republican nominee) Kansas.
If anything Lieberman is the weaker of the two. And it would be far better for Democrats to have him drop out.