So during the beta period I 'pinned the app' so it doesn't close or stops me from accidently closing it. With this it didn't close down near the end of the beta (at the start it did but it kinda stopped after an update they released so I can assume they fixed it) unless I did it on purpose. For the last week I had mined in constantly with no problem! It should just run in the background nicely :)
p.s. they will be fine tuning it so if it does close in the early days im sure they will fix it soonish