I have a 2006 Dodge charger RT Hemi, it recently was over heating. It cut off recently and would not start back up. The mechanic tells me the engine needs replacement. Is this my last alternative,???

There is a crack in the radiator and the
number 6 and 7 cylinder aren't firing up,
there was some rust from water under the
hood on the passenger front side, and it
over heated with smoke coming out 1day
before cutting off. The mechanic who I
really don't trust, did a diagnostic test to
find out problem, a "pressure system check
on the radiator" that's how he found the
crack. So all im asking is that a cracked
radiator, on a dodge hero, means new
engine??