Stalemate?

[Lisif Deoral]

I thought that stalemates were virtually impossible in SE4 - at most, a game becomes too long and too boring to be concluded, but a side will eventually get an advantage.
But...
Should someone (in multiplayer, of course) manage to "seal" a system by closing every warp point connecting to it and building a System Gravitational Shield Facility, is there any way to prevent a stalemate?
Intelligence might be used, but only if you can still interact with that empire...