There's way too many variables to categorically state who'll leave and who won't. A lot will depend on where we are at the end of this season, if we miss out on the play-offs or lose in them and are still in this league then we'll remain part-time. In this case we'll defo lose Boyes who stated when he joined that he'll only stay if we go up and go full time. Of the rest it is unknown how many want to go full-time, some will earn more doing a day job + whatever they earn with us. Some may see it as too risky and I'm sure there's other reasons why they might remain semi-pro. I'm sure we'll lose some.
If we go full-time then we'll obviously lose any players that want to stay part-time. In this case we may also lose players offered better deals elsewhere but again there are variables like potential extra travelling and if they'd be squad players or first team players etc.
As far as S&H poaching players again it depends if they think they can improve the current squad at Grimsby or if they know of players they think are better that are available. There's also the factor of loyalty to S&H if they do target our players, I'd guess the ones that followed from Ilkeston, Sleath, Church, Murphy and Newsham are pretty loyal to our former managers, but then in the couple of years they have been here maybe things have changed. Of the rest who knows how many would want to go play for S&H.
I notice people specifically mention Pearson as 1 that will leave. I have my doubts, do S&H think that he'd improve Grimsby's defence? does Pearson want to go full time? If he does and we went up went full time he may stay with us? If offered terms by both he'll have another hour and half travelling each way from his Norfolk home which will be a big factor I'd have thought. Apart from Boyes I wouldn't say anyone will definately leave and if things work out right even he may stay.
Things are never as straight forward as who we think is capable of playing higher...