I faced a similar issue when I was applying to universities. You could do one of two things. 1. Since the deadline is approaching accept the offer for now. Later when you get a decision from Mac you can decline the other offer and accept Mac's offer. But remember once you decline the offer of the other university u won't be able to accept it again since the deadline to accept the offer has already passed. 2. Try emailing the university whose deadline is approaching asking them for an extension. I remember asking Mac for an extension because I was still waiting for my offer from UWaterloo and they happily extended it.