The first one is used colloquially, but grammatically speaking, you should usually use the subjunctive mood for the second verb, i.e. بشود/شود:
.یه روز میاد که هر چی درده تموم بشه/شه
Regarding the second sentence, note these subtleties:
پیش خواهد آمد = will happen
خواهد آمد = will come
که هرچیزی دردناک تمام شود = that everything will end painfully
که هر چیز دردناکی تمام شود = that everything painful will end
A more literary form can be:
.روزی خواهد آمد که تمام دردها تمام شود