I think that the next game is going to be about the construction of another Mass Relay.
It doesn't make sense that if they had a standby that they would use the Second Mass Effect to just tell about a Huge Reaper and a recruiting process if there was a Second Relay some way. They said at the end "we'll find another way" not we have alternatives.
What Harbinger had the Collectors doing and what the other Reapers were doing aren't mutually exclusive activities. Nothing about building a human Reaper does anything to get the other Reapers back from dark space and so it's failure wouldn't directly impact any endeavour to that end.
When Harbinger actually said was: -
"Pathetic human. You've changed nothing. You have merely attracted the attention of those infinitely your greater. Those you know as Reapers shall be your salvation through destruction. You have failed. We will find another way...releasing control."
It's all there. Stopping the Collectors didn't change their plans, just caused them to target Earth first.
I suppose it's also possible "You have failed. We will find another way...releasing control."
was all directed at the Collector general rather than Shep, but it makes little difference either way.
Competitive multiplayer wouldn't be something I'd be interested in, but the game is almost screaming out for a co-op mode. One person could play as Shepard and make all the decisions, while I could play as Garrus. I'd stop playing singleplayer altogether and I'd just stick to being Garrus 100% of the time.
So you'll spend 90% of the time hanging around in one spot, waiting for the other player to come talk to you?