Deep Impact miscalculation ?

In http://tinyurl.com/9en2s it is pointed out that " Cosmic Crash
Won't Destroy Comet or Earth ".

It occurs to me that there may be a signifcant problem with the
analysis.

I assume that the calculations are made on the basis of change in
momentum imparted with the collision of bodies.

Nevertheless, other factors are involved.

For example
1. heating~~~ outgassing ~~~~ ' thrust through evaporation ' ???
!!! ???
2. Changing the surface, and hence the albedo and hence causing
futher outgassing as the comet approaches the sun ??? !!! ???

My concern ?
... merely that considerations are based soley on the tranferrence of
momentum between the space probe and the comet.

Am I talking nonsense ?

RL