Yes, you can always call "next METHOD" to pass the buck to the
next method in the list of candidates. Though an AUTOLOAD
is going to be pretty far down the pecking order, because Perl will prefer all declared methods over all wildcard methods, and autoloading is one form of wildcarding. So only an AUTOLOAD in a parent class (or a sibling class, since these are "next" semantics) is possible in the remaining list of candidates.
Though as for get_* and set_* methods, those would be non-standard in Perl 6. Perl's accessor methods will not be split into get and set methods. Rather, they'll be single methods that are lvaluable if you want to allow setting.