Anakin understood Obi-Wan’s underlying motivation for asking that. He’d asked that very same question so many times. Whenever he asked that around Padmé she, too, understood his fear; and she always answered she would find a way to find him again when everything was said and done, on the other side of where ever it was Jedi went to re-collect their consciousness when they died. That helped calm Anakin’s mind, but what would calm Obi-Wan’s?
Couldn't they stay here forever?
“There is no fast rule. Some people are here for a few months and then they disappear. Some have been here years. One boy tells everyone he’s been here eight… A few months ago, we even all glimpsed possible futures ten- twenty years from now… Some people leave and then return.”