Norwegian have quietly disposed of a number of NG's during the Covid shutdown and more importantly turned a profit on them, with the MAX stating certification flights the last couple of days, barring anything truly unforeseen, then the FAA grounding order will be lifted in due course and although EASA will want further modification such as synthetic airspeed it wont require that prior to RTS in Europe, Boeing will be granted a likely 2 year period to comply.
With low flight demand and low fuel prices the savings in flying a MAX over an NG are not massive at the minute but it wont be like that forever.
Norwegian have brought an additional 12 aircraft out of storage (and 200 furloughed pilots) making an active fleet of 20 and start flights to LGW & EDI again on the 1st of July, a further ramp up is planned for September, long haul from LGW will follow but not until the US CV19 situation improves.
I think the idea that 'people wont fly on a MAX' is overblown, it was safe before the problem, the problem appears to have been fixed, they have 18 parked up in Europe, my understanding is that Boeing will re deliver these aircraft as 'new'
The new majority shareholders have a vested interest in getting Norwegian back in the air profitably asap.
Ryanair's plan to base 15 aircraft at LGW (and creating a squillion new jobs) will nudge them along.