Usually it’s a good moment to capture the movie also to file when the DCP will be created. It’s simply careless not doing this. The lack of it can’t be compensated easy. So your client will realize that it’s cheaper to create a file version too in the DCP creation process than doing BluRay encoding from a reverse engineered master.
A genereal question comes up, what kind of DCP is it? Is it encoded to JPEG2000 or to a non DCI-conform MPEG MXF?
If you have access to Pro Media Carbon & the DCP is not encrypted you can try one of the following routes:
1st route = conversion via ffmpeg to V210 at 10bit
2nd route = conversion via VirtualDub (with ffmpeg input plugin) to any other AVI codec (depends on the installed codecs, sadly 8bit processing only)
For JPEG2000 sources you must convert the color space from CieXYZ to RGB color space. I have in mind that this can be done by ProMedia Carbon. FFMPEG sadly has no XYZ to RGB conversion fiter.
ProMedia is sadly a very expensive tool but may it will earns its money if you get such sources more often.
Andreas