If all the claims in the patent are rejected, the patent gets nullified.
The proceedings of all reexaminations are made available to the public on the USPTO’s public PAIR (Patent Application Information Retrieval) web site.
Inventors themselves also file requests for reexamination.
Such requests may be filed before the inventors sue another party for infringing the patent, to make sure that the patent is valid in light of any prior art they may have discovered since the issuance of the patent.
If any claims are rejected in light of the new questions raised, then the patent owner can narrow or cancel those claims.