Most of the Leeds Fans that were going will presumably already have booked and paid for their accommodation and travel.

Especially with Toronto deciding to isolate the whole team? Would they get sanctioned!

In the absence of any guidance or leadership from the RFL or Super League, Leeds did the only thing they could do.
Given that it was still a unilateral decision, the process for that still needs to be applied and any sane organisation will conclude that the club took the only appropriate measure available to them. The only question is whether the RFL or Super League are indeed sane organisations.

Should take SL to Court for attempting to send Leeds to France and risking further exposure to Leeds players, Catalans players, match officials, aeroplane passengers and many more. Plus potentially leaving Leeds stranded in France! What sane organisation would try to force that?

Remi Casty has summed the situation up nicely "I'm not sick, I'm not afraid of being either, but I don't want to catch this virus and pass it on to someone more fragile,". He's told the club he's self isolating so not training or playing. Leeds would surely give a similar argument for not travelling

The RFL should have suspended competition earlier anyway - especially any trips through airports and overseas. This is all a load of crap. Leeds have done the competition a favour, if anything they should get extra points for common sense.