If you have paid money for StaffPad and its in-app purchases, only Apple can take that away. So even if the new owners decide to discontinue the product (highly unlikely), you still have your Apple purchases. You might not get any future updates that make the app continue to work with the latest iOS. If this happened, I would just never again update my iPad. (I have no idea how things work on the Microsoft side.)
Yes, the problem is that at some point an iOS update will invariable break that app ... and if there isn't a living company behind it to fix it, then all the investment is lost. (Not updating you iPad isn't a good or realistic either, in the updates sometimes carry essential security content).
I don't think there's any need to panic, but given the investments we have in the software (and for some, critical workflow), this really needs to be handled transparently ...