They still have a role. Just not a role in Mech and Armor formations.
The whole saga about M777s in Canada is both interesting and serendipitous and based on the development of needs as Afghanistan went along.
With the move away from "heavy armour" - read tracks - in favour of light - read wheeled - we bagged the SPs without any project on the books for replacement. There was an unfunded "Future Indirect Fire Capability" project in the hands of DLR by 2004 to explore where to go next and when you look at the briefing slides every gun was a version of a wheeled SP. The M777 had not been fielded.
By 2005 CLS redesigned the artillery with a mandate for a lightweight towed howitzer with precision ammunition as Afghanistan was on the horizon. We lucked in getting 6 M777s on FMS from the Marines with 4 destined for Afghanistan and two for training. When things got rocky in Afghanistan in 2006 we exercised the option for 6 more FMS to be able to deploy 6 and train on six.
Parts were an issue. The US was great in looking after our needs but Afghanistan was rough on the guns and the production runs were still quite low. We bent two which was fortunate because we leased two to replace them and were using the bent two for cannibalized parts until they finally went back to the manufacturer for overhaul.
Running maintenance was always an issue - particularly getting parts and getting the guns out of the field where they could be properly serviced at 2nd line. There came a point where a third UOR was generated for 16 additional guns because by then the M777 had morphed into our operational gun and the maintenance issues and shuffling the guns around the country from one regiment to another for every roto was getting out of hand.
That UOR was eventually cancelled in favour of a full on funded project in 2008 which brought in 25 additional guns and properly managed support program.
Long story short, the vision in 2000 - 2004 was to support our mech forces with a type of wheeled SP and our light forces with the LG1. 2005 and Afghanistan brought us down the road of ever increasing number of M777s. Funding priorities after Afghanistan have ever since forestalled any move to a more balanced artillery structure to suite a mechanized force.
In fairness, the M777 also became the standard gun for the Stryker BCTs. It's a fairly recent development to move them to a wheeled SP.
I like the M777 as a light gun because it can be heli-lifted in theatre. I believe the requirement for that capability still exists in certain light forces, and as long as it does the M777 will fit the bill nicely. Air transportability into expeditionary theatres is a red herring. By the time that you add the gun tractor to the gun, it will take up the same space as a wheeled SP on a transport aircraft. Airlifting ammo is a much greater logistics burden then the gun, tractor or SP.
As long as we have mixed forces of both mechanized and light infantry, we need two artillery systems to support them properly. (actually more when you start adding in loitering munitions and long range rocket systems.)
I'm firmly in the camp of keeping all of our remaining M777s but allocating 18 of them to one light regiment to support one light brigade with the surplus going into spares and training locations. We should not go below the 33 that we have. All of them are necessary to keep an 18 gun regiment and the training system fully supplied.
What we need then is two 18 gun regiments worth of wheeled SPs to support two mechanized brigades, plus the usual spares and training guns which would put us in excess of 50. And no, I don't see that happening but that's what's needed if you want to play the game for real.
And boy do these threads ever amble. Have you looked at the C3 replacement thread recently?