You can look at Alcasthq for various guides on how an endgame warden build might look like.
But my best advice is: Just play what you consider fun and explore all the skills!

Wardens make good healers as they have their own hots and strong heals and are thus less dependant on the resto staff.
Most healers will have a destro staff on their backbar to support their group with ele drain and deal a bit of damage with blockade etc.
But keep in mind when you join a group as a healer, people will expect you to fill this role and only deal damage when healing isn't needed.
There is no big niche for a dps with a bit of healing, even though as a magicka toon you obviously have similar stats and could do it, it isn't needed or expected in dungeon groups.