IB Undergrad Dilemma

First I will start off by saying this is purely hypothetical and does not personally apply to me, but it is something I thought of while viewing the forums.

So here is the dilemma. Person A secures a sophomore IB internship, lets say at the MM/BB level. Now that internship may or may not convert to another internship for junior year. Now on the other hand other MM/BB investment banks are extending junior internships offers over a year in advance. Now assume this person applies to such an internship and gets an offer. To play it safe he/she signs with another bank for junior year. (rather than waiting to see if that sophomore internship converts or not). As it turns out Person A is in fact given a return offer at the sophomore bank. What would you do if you were Person A?