That really sucks for the kid, a reminder to all that things can go pear shaped at a moments notice. Hopefully he is taking solace that the treatments are working. It does kinda suck that there can't be any kind of cap relief. We kinda experienced a bit of this with Tui Katoa, but it didn't affect us nearly as much, firstly, he wasn't a regular starter, secondly he was on minimum, thirdly it was mostly during the off season. If we had a regular starter, say Kiraz, go down like this, we'd certainly appreciate some cap relief.
Maybe they need to tweak that rule, for cases where a serious illness that wasn't principally caused by training for or playing the game, and which has a reasonably firm expected recovery time, or as in this case, lengthy treatment process, with sign off from the relevant medical experts, the team gets temporary cap relief.