The goal of the Forsaken seemed to very much be secure Lordaeron. By whatever means necessary. How much of this was directly Windrunner and Windrunner alone is pretty debatable.
There are clearly Forsaken that have some lingering civic pride from their living life. Somebody was maintaining that memorial to Terenas Menethil in Lordaeron. And beyond that I’d imagine having a kingdom of the living dead would just strike many Forsaken as a good idea. And yeah you’ll need more undead to shore up those borders.
There didn’t seem much outside of that as a plan and nor did there need to be. The Eastern Kingdoms have plenty of territories that’ll remain eternally disputed.
That’s what bugged me about BtS. I’d assume a Forsaken wouldn’t want to live in Stormwind for the same reason a human wouldnt want to live in the Undercity. What a live and undead person need and want in terms of habitation and quality of life are vastly different. Even if every Live Stormwindian/Undead Lordaeronian was cool with the other living within their borders - I doubt they’re going to enjoy themselves for long.
But apparently that was something just never allowed. Guess Hearthglen, which is just up the road from Andorhal, where all the playable races live in peace and common purpose, was top secret knowledge no Forsaken could ever know of.