Leap of Faith

It seems I will have to take a leap of faith tomorrow. I had a successful interview with NX Nastran development team. They told me that they are going to send me the offer by Tuesday as my other offer with Dassault Systemes expires of Tuesday. Now, they need some additional processing and the earlier they can get back to me is on Wednesday. So if I want to reject the other offer, I will need to make a leap of faith with NX Nastran. I don't know what I should do!