Depends on how fast you can recover and your prior long runs
I had been training to run 2:29 for Boston this year. Went out in 1:14 and crashed at 16 -- jogged in the final 10 for a 2:50.
I made the mistake of trying to get back too quickly and didn't take care of myself by getting massages and all.
Ran the Green Bay marathon in 2:47. Faster, yes, but not near what the shape I was would say I could do.
That being said, I had 22, 24 and 27 mile training runs leading up to Boston. And my fall marathon this year, I'll have had 18, 18, 23, 26, 26, 24 leading up to it. The 2nd 26 may actually end up being the Twin Cities marathon if I decide to do it with the first half racing (at HM pace) then jogging the 2nd half.