I think it only makes a difference on the hills. So it depends on what your terrain is like. And as Spokewench said and as you know, body composition is a really important part of the equation, and when you lose weight without being able to strength train, it tends to be disproportionately muscle that you've lost. When I saw your thread title, I honestly thought your question was about how much SLOWER you could expect to be before you have a chance to build your fitness back up.

My experience is that it will come back quicker than you think, WAY quicker than it took to build your fitness level to begin with. I really take all those formulas you'll read, with a grain of salt.

I think it's good that you're building your fitness up indoors. Less comparison to how you were before your injury, less head games slowing you down. By the time your weather's good enough for an outdoor ride you should be smokin'!