I've been using Signal and WhatsApp for while on a lineageos + microg, it works perfectly fine without going through microg, i.e. I don't use push messages though (using the constant background notification from Signal and letting WhatsApp do whatever it does to work around the lack of push messages).
I guess it uses a bit more battery, but I haven't noticed it in my case (n == 1...).
Yeah, I have a phone with neither Play Services nor MicroG, and Signal works just fine using its own notification delivery system (which it emphasises you should use at your own risk of it not working and slurping battery).
I guess it uses a bit more battery, but I haven't noticed it in my case (n == 1...).