QWidget and all derived classes are a core part of Qt 5 on the Desktop.
You can continue writing your application in exactly the same way as you have been doing with Qt 4.x.
We have promised to try to keep as much source compatibility with Qt 4.x as we can. And of course this includes QWidget and your application written in C++. This is not going away. Yes, the Qt Widgets module we have in Qt 5 is right now marked as ‘done’, which means we don’t have anybody actively working on new features for the module at this point in time. But this can change any day if someone has some interest or need to do more active development in this area.
$('.tooltip').css('display','none'); лучше использовать $('.tooltip').hide();.