Emilio, I am too -a low silver though, cause I credit my UA flights to a *A partner.
Added info: agents at the airport have more leeway than phone agents and should be able to rebook you on a AC code share, however, I have never needed to be rebooked in AC but it's possible, just do a search here in flyertalk on "orc united rebooked to AC" to see people requesting missing miles when it happens.
Last edited by mbece; Oct 26, 2013 at 2:29 pm