Right, if you later withdraw/waive your demand for the formal PEB, the IPEB's findings will be given effect (of course, it has to be approved by AFPC/SECAF, but this almost always happens).
In AF cases, there is quite a lot that can be done to extend the processing time...an additional note, towards the end of the year, they normally close down for a few weeks for the holidays. Given the backlog and new leadership at the FPEB, I can't say for sure this will happen, but if it does, it always creates a further backlog. That, with an appeal, could almost certainly place your final disposition towards the end of next year...if you have leave saved up and many of these issues line up in your favor, you could make 20 years.
Glad to help, I think its what anyone would do! You help fellow Servicemembers/Veterans!