Congratulations on completing Tyria with a Mesmer.
Now, I'm guessing you rarely play your mesmer because, 1) its hard to get into groups; 2) it is more of a support character (reducing damage or making others hurt themselves as they try to hurt your party); and/or 3) some of the skills don't seem to be as pleasing to use as skills from your other characters are.
Mesmers seemed to be (at least to me) more like in Canthas then they are in Tyria.
You've spent so much time and money on your Mesmer, it seems such a waste to delete him/her.
Ritualists cannot buy anything in Tyria

. But Mesmers can buy armor, weapons, items, etc. in Canthas.
The only reason to kill off your Mesmer is if you hate that profession; if you love being a Ritualist (healer/protector/spiker/MM/Spirit Spammer, etc.); or if you just don't feel the excitement or pleasure that you do from your other characters.
Good luck in making your decision.