Ongoing Reserves

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?

well you read all the pertinent information that is in the rulebook, so no need to paste rules.

the only rule I see is that if something is deep striking you need to let your opponent know when it enters reserves.

I looked up Outflank and it said that you roll when you enter from reserves, but not from ongoing reserves. Not sure if that means you cant outflank from ongoing reserves, or you don't have to roll.

If you were playing and I was TO I would say this based upon what I read.

If a unit enters ongoing reserves then it has two options. 1 is to walk in from the table edge. 2 is to deploy via deep strike, if it has the deep strike rule. If you plan to use the deep strike rule, then make sure and notify your opponent when it enters reserves.