Yes. That is a good point. I've tried the same where I've opened a document editor made an edit and then put it in background. Sometimes it lasts a day and sometimes it doesn't. I had wondered if there was a time out but as far as I can tell androids main criteria for killing jobs is ram memory based. It could also be device dependent. Main lesson there is if you are working on, say, a document, using android and you do not want to lose changes save them before moving on to something else. Btw, terminal emulator is run as a service. I've never seen it closed, no matter how long I've had it running in background.