Best Fourth Option I can see already sort of exists. DO NOTHING! if you wait long enough you get a game over and a message that the crucible was destroyed. rather then that, have the game jump to a new Cutscene with the Crucible and the Citadel being hit by weapons fire and Sheppard giving a transmission that the Crucible is not an option, and all we have left is to fight, survive, and rise above, Sheppard then bleeds out and dies.
sure, maybe include some BS about the Catalyst imploring a choice, and being visibly frustrated that Sheppard won't choose. maybe make the Reapers retreat from Earth being pursued by the allied fleet the entire to the relay.
The catch. one Reaper stays behind and disables the Charon Relay on the way out, and leaves the Reapers with the mother of all catch 22's their biggest threat is isolated, but will not be for long (the Citadel, already established as a Relay itself is intact.) and they will eventually have to deal with that threat while taking losses conquering the rest of the galaxy.
sure, maybe include some BS about the Catalyst imploring a choice, and being visibly frustrated that Sheppard won't choose. maybe make the Reapers retreat from Earth being pursued by the allied fleet the entire to the relay.
The catch. one Reaper stays behind and disables the Charon Relay on the way out, and leaves the Reapers with the mother of all catch 22's their biggest threat is isolated, but will not be for long (the Citadel, already established as a Relay itself is intact.) and they will eventually have to deal with that threat while taking losses conquering the rest of the galaxy.