[Kon-Peki]

> communication is probably the best tool I have

Without a doubt. Just make sure you are not being a whiny complainer about getting dumped on. Everyone you talk to will already know you've been thrown to the wolves - you don't have to remind them of it. But on the other hand, they will also see that you are trying and preparing and taking the job seriously: If things blow up on Monday they will blame your boss for leaving. If things go smoothly they will think it's because you took charge and made it happen.

(But also, spend some time thinking about a new job, because there is always a small chance you get screwed. The business world is cold and heartless sometimes).

PPS - it is entirely possible that the users do not yet know about the scheduled upgrade, either because they were never told or because they ignored the email or whatever. They might have some major thing going on Monday and can't have any downtime. Talking to them and asking about experiences and concerns will surface that. If it is the case, they will voices on your side in a call for delay. And! It will look good on your resume: "Improved inter-department communication, saving company $$$$/increasing revenue $$$$ by optimizing software update schedule"