That sucks lee, stories such as yours are the reason I dont play EQ or UO incase I fall into that trap.
My sister has been addicted to a similar extent to a diffrent service. This is an adaption of the chain of events that caused her to loose intrest, although she did this by herself and i dont think she intended it.
My advice would probably be this (* - big fucking asterisk)
* Take him off on holiday, good time etc... at least a week, pref. 2. Keep his mind off it, distract him etc. (this is really the only thing that unaddicted her, so the following are just things ive added that I think will work, read the asterisk). This will disguise the fact that your removing eq. (yeah, I know, its expensive)
* While shes away, have one of your more technical mates come round, change his password, uninstall EQ, cancel his account. If you really want to make sure he doesnt go back on, install sub7 or WinVNC and keep an eye on him.
* When he comes back, dont make a scene if you possibly can, i.e. dont tell him youve removed eq, just dont lie about it, just act normal and sofourth. If he comes downstairs screaming about how his EQ has been royally fucked then be straight and brief with him. Try not drawing attention (possitive or negative, direct or indirect) to everquest and his going cold turkey from it if you possibly can. The last thing you want is him drawing attention to himself with it, as he may use it to manipulate you/your mother into restoring it, or otherwise using it as a tool.
* All being well, his life will get back on track. Bonus points to him if he realises how addicted and sad it was and vows never to get so addicted.
And now a disclaimer:
*I DO NOT know if this will work. Its to the best of my knowledge and I could be utterly wrong. My only assertion is that it is made in good faith, but may not work at all.
EDIT: Reminder, Ive got no garuntee that this will work. This stratergy has just been made up from events that ive seen work on an addiction. Perhaps, if he returns home still raving about EQ, it might be best to let him continue and find another plan.