The replacement sash was waiting for me when I came back from my two weeks out of town.
It didn't include instructions on how to take out the old and put in the new, but with a hint from an online friend we finally got that figured out. I have no doubt that we could have also gotten instructions from their customer service desk, but I didn't call until after they were closed and of course I didn't want to wait until the next morning to do this. What, me? Impatient? Nahhhh.
Once we knew the trick it took me three seconds solo to take out the old, and 3 minutes with Partner's help to put back in the new.
And so while the window really shouldn't have broken in the first place (and we still have no idea why it did), Survivor Windows (sold through Lowes as Reliabilt) gets a solid A for customer service because of their immediate action to send us out a replacement sash without making us jump through hoops, even knowing that the windows were 9 years old and that we didn't have the receipt, and they didn't even challenge me about or ask for pictures to back up my claim that the window broke all on its own, as evidenced by there being zero damage to the screen or inner pane. They would have earned an A+ had they included installation instruction, since it was not at all difficult but it was also not intuitive.
I'm especially happy with their customer service when I compare it to what my dad is going through with MW Manufacturers Windows, also sold through Lowes, to get them to fix or replace a broken window that he bought only a couple of years ago. If I understood his tirade correctly, they're basically saying "oh we don't have that part that broke and we won't replace the whole window so you're SOL."
I'm still no big fan of vinyl windows overall, particularly to replace original wood windows in old houses. I'd still much rather have the windows that were original to this house, and just fix them up and add on good quality storms and screens but the deed was done when we bought the house. But now that I have vinyl replacement windows, it's good to at least know that they're from a company that will solidly back up their product.