I remember in old versions, you needed to suppress IC you crashed, to prevent system alerts, and you'd dedicate your Hacking Pool to this. I'm wondering though, is this necessary in the current edition, or do crashed IC 'go away', without you needing to focus on this?

Well, as far as I understand, IC are just crushed like any other programs; other IC (like the one in Unwired) may check to see if their buddies are running and either relaunch them or change alert state.

"Hey Bob, Bob, you still online Bob? Bob? Now's not the time to go offline for a patch, that's in fifteen seconds. Bob? Uh oh. BOB'S OFFLINE! SOUND THE ALARM!!!"

Singularity Encore, Unwired pg 71 for those interested.

There is the Nuke program in Unwired that will freeze rather then crash a agent/IC if it reduces its pilot rating to zero.