From what I'm aware of, the council (even as leaseholders) have no say in what rent the Warriors are charged & nor can then withhold the lease to any new stadium owners because of it.
They can refuse the lease if the new stadium owners refused to allow them to play there as that's in the terms of the lease by all accounts
I have no desire to see the rugby club crippled, but if the stadium is losing £1.5mill a year then it's only right that the new owners look at increasing it's income streams - as well as renting out offices, function rooms, concerts & so on it's only right & proper that the rent paid by the tenants is also reviewed.
Those tenants do include Latics though & so any rent increase should be applied equally to both clubs. That's only fair, but it's also only fair that Wigan RL pay a going rate for use of the stadium