This is has to be one of, if not the biggest reasons I think the whole galactic readiness being tied to MP is the stupidest idea they ever came up with. JMPO. Then, adding the fact that your galactic readiness actually decays over time pushes it right into the moronic realm. My copy of ME 2 sat for months on end without being touched, then I decided to go back and play through it again... I did this 'cycle' several times, play - give it a rest, play... How much will I feel like doing that with ME 3 if I know that a factor which contributes to the ending of my game is tied to a no longer existent MP group? As it is now, I have very few people on my F/L that play MP, they're all playing SP.
Exactly my thoughts. Hopefully when the multiplayer does die out, like @Ruthless said, they will patch the game giving us 100% Galactic Readiness as default - or at least a new way to obtain it. Otherwise I'll be pretty ticked.