I can guarantee I won't be going back to reddit on mobile if they go ahead with the API changes. I may occasionally use reddit on desktop but 99% of my reddit usage was on mobile via Sync.
Once they get rid of old.reddit (which they inevitably will) that will force my hand and I'll have to fully move to Lemmy. As luck would have it, the developer of Sync is considering re-purposing it to run on Lemmy which would be perfect for me.