I'd agree to seat Florida and Michigan according to the rules the Republicans are applying to those states, which is that the number of delegates is reduced by 50%. This is totally in line with the rest of the Democratic party's rules: the later your primary is, the more delegates you get.
The reason to take this gamble is what happens if Michigan gets their do-over. Sure, it's fair. But Hillary probably wins it and because it's in June it gets a disproportionately high number of delegates.
Better to give her back 20 delegates or so than to risk giving her 50. And the PR points might make those numbers back in Pennsylvania.