From what little info I've gleaned of late. The Inlander is on very thin ice and could 'go' at any time.
The Westlander has a slightly less shaky future, despite the rusty condition of some of the cars, and to Transport Minister Emerson's credit he is working very hard to increase the number of cattle trains right out as far as Quilpie. Obviously with the western line in reasonably frequent use, the Murwillumbah (Mull'bah) example is not applicable.
The Spirit of the Outback (SoTO) will need a refurb in the next 2 to 3 years, especially the First Class club car, if it hasn't already been done since I travelled on it 18 months ago.
The Sunlander as we currently know it will be gone by this time next year, and when I travel on it (Queenslander class) next April, it will be only one service a week. Sunday out of Roma St and Tuesday out of Cairns.
Not sure what the frequency of cattle trains are, but I still doubt it exceeds more than 2 per week/52 weeks a year on average as far as Charlieville. Issue is the track quality for such services doesn't need to be maintained to same as required for Westie and all that will happen over time is it will be slowed down. One way or another I still see this service on borrowed time. If LNP don't cut it, ALP will when they eventually get back in.
Inlander, problem with this train is that there is not alot along the route, it has even less tourist potential than the Westie and most people going up that far would drive anyway. For locals the train is of limited value due to its slow speed and most of the population are a fair way out where plane is far more competitive. I'lve also heard along recent years that its not uncommon for the Inlander to be terminated at Conclurry due to track/cogestion delays and/or lack of numbers.
Either way, the issue will be what rolling stock is left after the retirement of the L cars. The inlander being based in T'ville will make it difficult to serve with a limited fleet of rollingstock as when not used by Inlander it can be used by no other.
Either way, by end of next year, I suspect there will be some significant changes to the current Traveltrain timetables, although a election is not far away so perhaps the changes will be more controlled. Time will tell.