Update. Same errors after expansion download. More detailed below.

So. Thanks to patcher keeping whatever it was able to download and despite constant server connection drop I was able to download Heavensward and all patches. Getting it all in 0-100 mb pieces was pain, let me tell you.
Did some testing on how game behaves.
At peak hours on launcher login screen most of the time (~70%) it still keeps giving same old [30413][10009][10019] error codes, stating it could not complete version check. Sometimes (~30%) it accepts ID&Pass and starts game. On world selection, character selection and character load it sometimes (~40%) crashes with 90002 error. BUT if it manages to load into actual map with your character, it's stable - played ~2h, did some roulettes, works fine and lagless. On game restart it goes through same painful error and crash crap again though.
At non-peak hours the [30413][10009][10019] and 90002 still happen BUT much less frequent.
So game itself works for me. Log-in is totally messed up (takes up to 30 mins of retrying to load into game at peak hours)