The word ‘If’ is doing a huge amount of heavy lifting there…
Unfortunately, CMAL are in a pretty dire situation fleet-wise. The small vessels are fine, but the situation with the large vessels is incredibly difficult to deal with. If the Glens had entered service as planned, CMAL would have had some breathing room, but now they're relying on the Turkish vessels entering service without any major issues.
Keeping Caledonian Isles (or isle of Lewis if Caley is dead) makes a lot of sense.
I've looked around, and it seems that Isle of Lewis is more than capable of handling most of the large vessel routes without any problems. The only issue I can see is that she'd be quite low on passenger capacity for Mull, but it's not the end of the world if Caley Isles is indeed headed for the scrapyard.
With 15 large and mid-sized ships in the Calmac fleet, with around 30 year lifespans, they should have a rolling programme, replacing one every 2 years, not this mess!
Honestly, what happened to CalMac from the early 1990s onwards has been nothing short of a disgrace. It's not the fault of the management, it's just a simple lack of investment from all quarters, combined with a failure to modernise the operation to reflect modern realities.
I can give a comparison: I took the Alslinjen service in Denmark from Fynshav to Bøjden last year. The port in Fynshav had nothing more than a ticket machine, with the ticket office being available for use but unmanned. To enter the waiting area for cars, you could drive up and use an electronic tag (same as used on toll motorways or bridges/tunnels), use a credit card, or just scan a QR code on your ticket that you obtained online or from the ticket machine. When you entered the waiting area, you simply queued up as normal, and when the ferry arrived, the entire operation was incredibly slick: it can't have been more than 10 minutes in port. The crew waved most cars straight onto the ferry without checking tickets (as they'd already been checked on entry to the marshalling area) and only a few cars were chosen for a spot check of their ticket as it was possible to join the queue without passing through the entrance to the marshalling area.
In terms of check-in and so on, there's a 15 minute check-in across the board to be guaranteed entry to your chosen ferry. CalMac in comparison is at 30 minutes for vehicles, which really makes no sense for the ferries where advance bookings are normal and specific sailings have to be booked. CalMac are also still relying on staff manually scanning tickets rather than using automatic entry systems, both for vehicles and for foot passengers, even at the most modern ports like Brodick.