Anyone this stupid tends to be stubborn as a mule as well. I don’t see him dropping out.
The National GOP is going to run some pretty big, pretty intensive polling in Missouri (internal polls) on Monday, and Monday night the RNC chairman (Priebus) and either Romney or Ryan (or both, but I'd bet Ryan is the guy) are going to call him and lean on him heavily to drop out the race for the good of the party.
If Akin stays in he could cost Romney/Ryan the election.