If for whatever reason a unit enters ongoing reserve, what are their options for returning to the board the following turn? I understand that a deep striking unit that mishaps gets to arrive next turn via deepstrike but I don't see anywhere in the rules where this is spelled out. A flier with the Deep Strike rule flies off the table has to zoom back on the next turn. I found that rule.

This gets a little less clear when you consider a unit already deployed on the table that decides to enter ongoing reserve that has the deepstrike Special rule. DS says that the unit has to begin the game in reserve but it also says that when they go into reserve is when you tell your opponent that they will deploy via deep strike.

Could a unit deploy via deep strike turn two, then later enter ongoing reserve (for whatever reason), then return to the table via deep strike the following turn? Or does the unit just walk onto the table? Weird scenario but could it be possible?