The question can be interpreted in many ways. I could think that a friend who is making me choose between them and a promotion is not a friend worth having.
Suppose Al and Bob have been accepted to ycombinator. Things don't work out very well and 1 month out from demo day they're pretty sure they are going to bomb. Al gets a spectacular employment offer -- contingent on a start date before demo day. Bob doesn't. In fact, Bob has faith that they'll be able to make <metric of the year> if they try hard enough. Through no fault of Bob (and possibly no fault of Al), Al now has an incentive to throw Bob under the bus.
Suppose Al and Bob have been accepted to ycombinator. Things don't work out very well and 1 month out from demo day they're pretty sure they are going to bomb. Al gets a spectacular employment offer -- contingent on a start date before demo day. Bob doesn't. In fact, Bob has faith that they'll be able to make <metric of the year> if they try hard enough. Through no fault of Bob (and possibly no fault of Al), Al now has an incentive to throw Bob under the bus.