I'd rather have Morton. Fabs, Thiago and Morton is a damn good midfield even though Morton is still a baby - and he tackles (and loves to tackle he says) way more than Gini ever did (Gini isn't a tackler, he's a possession retainer, which is why I guess it's not working out at PSG - he brings little to the attack and they have all the possession they need).
I'm not worried about our midfield if Fabinho and Thiago are fit and available – any of our 3rd (more attack-minded) midfielder options, be it Hendo or Elliott, Jones, Keita or Ox will do fine, each in their own way. If Fabs is not available, Hendo must be to play at DM, otherwise we are a bit screwed (Milner can do a job there for an odd game, but that's about it). If Thiago is not available, until Morton's emergence we didn't have anyone else comfortable in the role of a "2nd midfielder" – Hendo was tried there early in the season and didn't convince, Keita can do a job, but we can't rely on his fitness for such a key position and this role stifles his best qualities. This is where we truly missed Gini – I don't think we comprehensively lose the midfield battle to City in that first half with him in the side instead of Jones, for example.
Now with Morton, I'm eager to see him tested against a proper EPL team that will try to put him under pressure – he looked so in control and unflustered against Porto and Milan and it would be interesting to find out where his limit is at the moment. If he aces through the next big tests, in theory he can replicate Thiago's role in the team, but that's a pretty huge responsibility to place on someone who just turned 19 and made his debut a month ago... And if he's not ready, then without a player like Thiago we will lose a lot of control and press resistance and our defense will be tested and put under pressure much more frequently.