Your TIFF is already an RGB image. It might be a still from a video that is chroma sampled.
Y'CbCr has no place in the TIFF specification. Y'CbCr is the currency of video land - in TIFF land they don't speak that language. RGB is a color model. Y'CbCr is a chroma sampling and video encoding specification (compression for video) that is a digital byproduct of other similar analog specs, like YPbPr, etc.
Neither of them are color spaces.
If your TIFF came from a video shot on an HD camera, it is probably in the Rec. 709/sRGB color space (same thing, almost). If it came from a PAL SD camera, it is in the PAL color space. If it came from an NTSC SD camera, it is in the NTSC color space. If it came from a RAW camera (like the Alexa, F65 or Red), then it might have its own proprietary color space (like Red or the F65) or maybe it's like a still camera RAW file (ArriRAW) which doesn't have a color space yet. Also, higher-end video cameras have LUTs, special-gammas and S-Logs that make things complicated.
To answer your question: The file won't lose information - but you might have already lost information in your TIFF conversion. Need more specific information for a better answer.