Better get it from official runescape website, don't download from any other sources. If you can't then I guess no luck to use mirror mode.
Anyway, the mirror mode on official runescape client is very buggy and crash very, very often.
Hmm, depends on how much you bought the account for..
Maybe you can try to bot out the investment from the account then see if it's still alive, otherwise if it was me, I would focus on your main.
"You probably need them for your ass"
Lmao, interesting perspective of a legit player.. The community is amazing on Runescape! Will probably do some of these soon