Lost root, can't upgrade either

[Chris.Nelson]

I have a Galaxy S5 (on Verizon) that I had rooted after buying and succeed in getting through one upgrade and reroot since then. I recently got notices of the 4.4.4 OTA upgrade. I found directions that said undo root so that the OTA would work. So I did. But the upgrade fails so I missed something. So I tried towelroot and it failed to restore root. I've since tried using Odin to install two different kernels and towelroot still fails. What is towelroot using to tell if it will work? Am I out of luck?

I have reasonably recent backups and I'm on the verge of doing a factory reset and starting from scratch. Is there a better plan?