Q: Since Apple stopped updating iPhoto will Photos eventually not work with iPhoto library later down the road?

No - Photos does not link to iPhoto - it uses Hard Links to the original photos - iPhoto and Photos are totally seperate

Someday iPhoto will quit working after some future OS upgrade - that will n=have no effect on Photos as it is totally separate from iPhoto

Photos saves disk space by sharing images with your iPhoto or Aperture libraries - Apple Support

LN

But it could be the case that sometime down the road that Photos will not be able to convert an iPhoto library and you will have to import your images manually. But we don't really know.