SCArmoury said:

He all,

How often are the Fusion champions changed? And do they become available again at some point?

I could easily see someone working towards a fusion champ and not making it. Should one keep the requisite champions in stasis for a next go around?

Thanks

The ones you can see now are permanent. You may be thinking of temporary fusions, which are organized every once in a while, like maybe once every two-three months, and are generally available for about 4 weeks. Generally there is at least some way to obtain all the necessary champions during that period. 

Looking at the last two temporary fusions, Skull Lord and Gurptuk, the former required 16 Skullsworns (farmable from campaign - but good luck getting 16 of them to drop!) and the latter was fused from rares/epics who could all be obtained from various events that were run during the 4 week period. But in many cases, getting the champ from the event required such massively high scores that low-level F2P players had zero chance of succeeding and even high-level F2P ones had to put a ton of effort in, if they didn't already have the champions beforehand. Personally I had most of the rares needed for Gurptuk, so it was doable, only needed to grind hard in a small number of events. 

And so far, temporary fusions have never been repeated yet - though some people have requested it, considering that past fusions included great champions like Rotos, Foli, Sir Nicholas. I doubt it's going to happen though - they don't want to bore the veteran players who have already done the earlier fusion. 

Though it does happen that champions used for one temporary fusion are used again in another, so if you go for a fusion but fail to finish it, it doesn't mean you should necessarily discard all the champions that you did get.