Black Spider your plan would require everybody not currently being invaded to just wait and see what happens.I see no reason for the Nords not to send troops where ever the Thalmor pop up.Even Cyrodil.
An independant Skyrim can still ally with the remnants of the empire.Trade can continue Nord troops could still join the legion(the Thalmor may whine but eff em)
So I do not have the sense of doom and gloom if the Stormcloaks win.Quite the opposite in fact The Nords untethered by the treaty should cause much dampness in Thalmor robes just above the thighs.
The thing is, two sides in a civil war don't usually work together all that well after the conclusion of their civil war. And Ulfric of all people is hardly the person who'd ally with the Empire after fighting a bloody civil war to kick them out of Skyrim. He might make a Hammerfell-Skyrim alliance and that would be a force to reckon with, but if the Empire can't stand against the Thalmor then I doubt a union between Ulfric's playground and a war-torn Hammerfell can either. And remember, defending for a long time isn't good enough. If no offense is possible then defeat is certain. It's only a war of attrition if the enemy also takes losses.
Contrast this with the current Imperial strategy. As long as the Empire stands, the Thalmor can't win. The Thalmor can't take on all of the Empire because sooner or later the invasion force will be cornered and have to face the Legion in open battle, and at that time the Thalmor force will lose. Thus the Empire can afford to bide it's time, which it is doing, and push Talos-worship underground. Officially it's outlawed but in reality, there isn't an Imperial law enforcer who cares about it.
Look at that Whiterun Talosian? He's been standing every at the cloud district and shouting his religious crap and nobody has bothered to put him in chains yet. At this point my ears are bleeding so badly that I almost wish someone would enforce the law, but nobody does. Nobody cares, which means Talos worship continues and the ultimate Thalmor goal remains foiled.
Meanwhile the country can build up and hopefully avoid more plot nukes until such a time where going offensive against the Thalmor becomes possible. The mainland is more or less safe from further Thalmor invasions, the Legion can rebuild, new spy networks can be created, and superior human reproduction can replenish the population rather faster than the Thalmor can rebuild new armies. The current situation looks bad, but appearances can be deceiving. Fact remains that the Thalmor can't hope to invade a unified Empire. They've tried once and it cost them their entire invasion army.