Bare with me, please, as I think out loud here and bring out the problems as I see them. The main question(s) have to do with these two parts of the two texts:
Future Fusion (Continuous Spell)
...When this card is removed from the field, destroy that monster...
Rare Metalmorph (Continuous Trap)
... Only once, negate the effect of a Spell Card that targets the monster...
Point 1: Chimeratech (being the Fusion Monster) is sending both cards from the field.
Point 2: Future Fusion's effect that destroys Chimeritech cannot be chained to, though Chimeratech's can.
So, thusfar, Chimeritech activates to destroy the two and Rare Metalmorph is chained targeting it. It resolves first and is targeting, now....
In order for it's second effect (that 1x negates a Spell Card) to work, Rare Metalmorph MUST be activated and targeting, but according to the ruling regarding Snatch Steal, it seems like it is acting as a continuous effect ("If you chain "Rare Metalmorph" to an effect like "Snatch Steal" that targets a monster, "Snatch Steal" is equipped but its effect is negated while "Rare Metalmorph" is active."), therefore, instantaniously allowing you to negate the spell card's effect.
So far, so good. Now sometimes Konami is adamant about plurals, and sometimes not (surprising since the Japanese aren't so particular with their nouns) So one question may be, does Rare Metalmorph negate ALL effects of the particular card, or just one ("... Only once, negate the effect of a Spell Card that targets the monster...")? I know this may seem a little silly, but you know how many rulings are based on the fact there is no "(s)" in the text. If it does negate the effect(s) of the Spell card, then it would be equivalent to a miniature Imperial Order and all will be right with the world.
However, if it cannot negate an effect that doesn't happen until both cards leave the field, then, even if neither use the chain, can it still negate the second effect of Future Fusion. In other words, if the entirety of the effects of Future Fusion are being negated when they leave the Field, it would be the same as Imperial Order and Premature Burial, or Royal Decree and Call of the Haunted...no problem. However, if it is "effect" focussed and not card focussed, it would not be able to negate it, as they leave the field at the same time. I guess the troubling part is that the controler of Rare Metalmorph selects when to apply the negating portion. that brings up a timing issue (to me). However, as I have looked at this and thought it through out loud, it appears that this aspect is less an issue than I originally thought.
Therefore, because Rare Metalmorph (once it has it's target) is a continuous effect that can be applied to any (applicable) Spell Card at any time, and the effect of Future Fusion that destroys it's target is also a continuous effect (not using the chain), then in all these circumstances it will be negated.
Sorry for the round about way of getting there, it just helps to think the issues and doubts through.