If you are truly in Limp mode, it will remain in the gear it was in when the trigger happened.
Until you stop.
After that, you will only be given 2nd gear and reverse as usable gears.
There are many other limitations that people call "limp" mode, but which do not involve the transmission.
(a leaking intake hose, for example, will prevent the Sprinter from developing "boost" ... but it will still happily use all of its gears)
--dick