Its not so much wether you agree with anyone, it's more about how difficult you want it to become and how much time you have to spend on this. You were asking for advice and opinions. They can differ as you may appreciate. But both replies agreed that it would very much depend on how the market is and how fast you would be able to re-rent.
If your friend is able to rent it on July 1, again collects the security deposit from a new tenant (half month rent in BC) and starts collecting rent, he is not at a loss.
and that's how it will be looked at if either your friend, or your tenants that cancelled would take any action regarding this issue.
ONLY if your friend can't rent it July 1 and can prove this with all necessary paperwork/proof you might/will be entitled to keeping the security deposit. As far as collecting any other rents, well there is small claims court, and again you will have to have it all documented with necessary proof in order to demand anything, and in case you would be entitled to more, you would still need to collect it from that tenant. (When granted, you would still be responsible for trying to collect)
I understand your friend is upset, But as much as you don't want to be "screwed" (and don't get me wrong, no landlord would like that) my question would be, Is this worth your time and frustration?
That's what he has to figure out for himself.