If you bought a MKIII when it was released and Canon released a MKIIIa a year later, what would your reaction be to that (regardless of the reason for the new release)?
Mine would be to evaluate the MKIIIa and determine whether it's compelling enough to spend money on. If so, considering spending the money. If not, don't. Just like any time I buy anything.
If something is compelling, and if I can afford it, I'd rather get it sooner than later.
If something isn't compelling, eg if the MKIIIa doesn't bring anything unique to the table that I feel I absolutely must have, I'll keep using the MKIII until it breaks or until something else comes around which does bring something to the table. If MKIIIa brings only GPS or WIFI, I will not be interested; those aren't compelling to me. If it brings 35MP, I will be interested and will consider buying.
The fact that there is a newer model doesn't somehow break the one I have now. It still has everything I bought it for.
Let's look at it another way. Say someone had a D7000 and wanted to shoot FX. When the D800 debuted, they jumped on it and used it. Then the D810 came out. Would that person be willing to trade out all the photos they took over two years with the D800 (i.e. have taken them with the D7000 instead) in exchange for having later bought the D810? Possibly, but only if they didn't buy the D800 for a compelling reason.