That cut looks good! I didn't think the long ass tool would hold up, but it seems better than expected. I bet it was squaking like a bird. I've done a lot of parts that deep but it's almost always in styrofoam, not anything more dense, and even then it squaks. lol
Anyway, you can re-start in the middle of a program but you'll have to enable the setting for it (I don't remember the setting number, but it's called "program restart"). The program pointer will then scan through the entire program in order to estimate where to position itself in XYZ before picking up wherever you desire. It has to scan through the program to ensure it has the correct tool, H-value, internal variables, etc.
Depending on the machine's age, the scan make take quite a while. The older mills using a CRT display seem to process like 20-40 lines per second so it may take a looooooong time to get through a program like yours. But it would surely be quicker than running the whole thing again, that's for sure!