Well lets look at a couple of Boras clients that he ended up dragging into Spring Training without a deal. The 2 that pop into my head right away are Jake Arrieta and Bryce Harper.
Jake Arrieta ended up signing with the Phillies on March 11th. He didn't end up making his first regular season start until the Phillies 8th game, but pitched really well, having a 2.18 ERA in his first 10 starts.
Bryce Harper signed on February 28th but I think was ready for the season to start after having a couple of weeks of spring training ABs.
So it seem like Boras is more than willing to let this drag out well into Spring Training if needed and while I do think when one of them signs things will start to move a bit quicker as teams get weeded out for the other guys, I don't think it will be a dam breaking necessarily.