The residence issue will definitely come up he files for US citizenship. However, he already stated that the citizenship is not of a concern. His only issue is getting back into US, and the re-entry permit will allow that.
Hi:
I was not referring to citizenship. A GC and a REP do not guarantee entry to the US. Even if you have only been gone for 4 months, and e.g. return to visit a friend (with a GC and REP), it is possible for the officer to determine that you have abandoned your status given the weight of the evidence.
A REP is useful when you have a VALID REASON that accompanies it e.g. tending after a sick parent, going on a cruise around the world are the cliche examples. However, if someone takes a REP, closes most of his US bank accounts, sells his house, buys property in India, sets up accounts there etc. etc., an officer may very well determine upon a subsequent visit that he abandoned permanent residence (even if the person filed taxes and has a GC/REP).
Unfortunately, case law indicates that it is not as easy as just following some basic requirements e.g. file REP, pay taxes, you're fine. Think of it this way - the GC is intended for you to reside permanently in the US, with all absences being temporary. A REP provides documentation for a longer, but TEMPORARY absence. If at any time, even before the REP expires, the weight of the evidence indicates that your absence is no longer temporary and that you are RESIDING abroad, you may have abandoned status.
Of course, if the POE officer determines that, all GC holders have a right to appear in front of an immigration judge. But the person's chances of success will be much better if he has properly preserved status.
Again, the poster should contact an immigration attorney who specializes in abandonment cases. It is a fairly tricky area of immigration law and many immigration lawyers do not touch it.