I would never recommend putting yourself at risk, but ghosting the person after lying that you'd like to see them again is just a dick move.
I'm on lemmy.ml because my application was ignored (or not accepted, I don't know) by the smaller instances I've applied to.
That's why I'm here, specifically. I had vacillated between Lemmy and Squabbles until I saw Sync was coming here.
Sync going away -- and now coming here, yay! If they're giving their users the finger, and there's a reasonable alternative, why would I stay? I was mainly there for the communities related to my interests (their size, not their mere existence), and those are present here and elsewhere in a growing capacity.
I did like AskReddit, though, and I'm not sure if Lemmy will ever get anything like that...
There may be some impact, come July, when the third party apps stop working. However, I have to imagine that the vast majority of mobile users use the official app. Quality may take a hit, with the loss of some mods and mod tools, but Reddit will be just fine. Sadly, Reddit rates too highly on content, users, and resultant utility (for many communities) for most users to completely abandon it.