You shouldn't be worried about if he is to powerful for your monsters though in this case. You can always fix that, you should make sure he is not outshining the other players, as long as that is not the case, just throw something heavy on them.
First flaw I spotted was that after the first level of Forsaker he is not allowed to progress any further in Monk anymore. And don't forget as Mistah J pointed out the incompatibility between Vow of Poverty and the Forsaker's Signature Weapons ability. Furthermore since it's an Exalted feat if he commits any evil act he loses Vow of Poverty completely as well until he receives an atonement (which would cause him to lose his Forsaker abilities). In addition Vow of Poverty as well as Fast Healing are suppressed in any anti-magic field besides that of the Forsaker himself, SR does not apply.
Now what can we throw at him, let's start simple, before he reaches the point where he does need to sleep, eat, drink or sleep, have him face troubles with that. Damage done by hunger, thirst and suffocation can't be removed by any other means than solving the problem.
Later on my favorite in this case is sending him to another plane. Basically once the Forsaker ends up on a plane he's stuck there since he can't voluntarily use magic to escape the plane, even if he finds a portal, the portal would probably be considered a magical item in some way.
Send him to any strongly chaos-aligned, or strongly evil-aligned plane would force a -4 on all Charisma-related and -2 on all Int and Wis related checks.
Throwing him in the Plane of Negative Energy deals 1d6 negative energy damage every round, which slowly wins from fast healing 3, and it is not unlikely that the plane will simply render fast healing ineffective. Negative energy is not subject to damage reduction or any kind of energy resistance. It is also not a spell, so spell resistance does not apply. The effect also does not require any kind of save. There are only two ways to protect yourself, both rather simple. Have negative energy protection cast on you or find a pocket in the plane where the negative energy trait is only mild.
Unless he obtained outsider status, throw him in Hades, forcing a weekly Will save DC 10+numbers of weeks spent in Hades or be entrapped as a petitioner of the plane. Could be really fun if there is no way out. Petitioners lose all memories and class levels, and do not want to leave the plane. Miracle and wish can undo this, but he probably would still have broken his Forsaker code, and since he has been evil lose any Exalted feats. Hades is also strongly evil-aligned so the save being Wisdom based has a -2 penalty.
The Plane of Faerie is interesting if you allow him to exit the plane, or force him to exit it, but it would cost a lot of time. Time passes seven times as fast on this plane, but the character is unaffected by this while on the plane. In other words, if you spend one year there you instantly age 6 years when you leave the plane. Assuming he has a maximum age spending to much time on this plane could kill him upon leaving it.
And finally this is the most fun. Have someone pull him into a plane of mirrors. Upon entering one of these demi-planes a mirror copy of him (excluding any mirrors in his possession) is created and will start hunting him down, reaching him after 2d20 rounds. The mirror copy is opposite in every way, handedness, alignment (and associated codes of conduct), except that it has darkvision 60 ft. even if the original doesn't and has only one goal. Killing and replacing the original, which is the only way the mirror copy can leave the plane. The original can leave the plane by exiting trough a mirror, but again these portals might be considered magical items, or maybe the mirror trough which he enters is destroyed and his mirror self find him before he reaches another mirror trough which to exit. The spell to enter a Plane of Mirrors is 5th level for Clerics and 7th level for Sorcerers/Wizards, and anyone using the spell may pull someone else in if they happen to be near the mirror.
And lastly, although I have no examples of such planes, you could throw him in a plane with the dead magic trait. While rather ironical this would even suppress some abilities of the Forsaker (including his anti-magic field, hehe). The only way to enter such a plane is trough permanent portals though, so the way out is the same as the way in.
All of the above can be found in the Manual of the Planes, and possibly partly in the Dungeon Master's Guide.
Also, psionics would only work if you use the psionics are different house rule. Normally psionics are subject to everything magic is subject to. Under this rule the Forsaker would be allowed to use psionic items and powers, unless you change this so I would not suggest this.
