Not sure where you live or what the job market is there. Going from programming Java to programming C is a huge step backward IMO. It may be nifty to have, but Java is in high demand. If they were asking you to do C#, that would be a different thing. Going back and forth from Java and C# is easy stuff.
Now if they want you to convert the C code to Java (you might suggest as much) then you may be on to something, and potentially become a company hero with the Code Convert Champion achievement earned
That all said, I would stick it out and stay with Java, get the raise in a year and carry on. Architects be Architects don't sweat that. Time served = Experience. Work it right and you can gain your own visibility. If it goes lopsided, you can always find work coding Java elsewhere.