I do not see K4 going anywhere soon even if / when Connie heads west. If I were in my 30's or early 40's and cargo was my be all and end all then Atlas maybe a consideration if I were not interested in an overseas contract making far more than domestic cargo.
A move to Atlas would beg two questions for me, the possibility of an upgrade is years down the road just like heading to a major carrier and is the few left seat years really worth it? Secondly, Atlas have a sharp management team but just do a google and it would appear also a high debt load unlike K4. As mentioned if the economy etc takes a trip south how will Atlas handle it?
Hopefully K4's EXCO can get a contract sorted in the near future with the help of continued arbitration and that should hopefully bring a more leveled playing field along with hopefully more airframes.
At the end of the day, individual situations and choices can only be made by that individual, for me with 15 years left the move to Atlas (or anywhere) is negated by the fact that the potential extra money over the period doesn't make it really worth while added to that starting at the bottom of the list and getting leftover lines and thus a decrease in QOL.