That delta IV heavy is a very impressive sight. but I see that each
booster section has ONE engine each. So I presume that ONE booster engine failure after launch wlll lead to a mission failure.
If that is true then what if there is failure at 30 seconds before booster separation, Can the rocket be configured and would it be light enough (fuel tanks mostly empty) to continue on 2 engines? (I know the central engine
cannot be the one that fails)
In the battle between Reliability and Man_Rated factors, is it better to
go with boosters with 2 engines each, so that you can lose one engine
and continue with the mission? as an example, reconfiguring the Delta iV
heavy with six engines means that the rocket could press on with 5 out of
6 engines.
Be aware that each of the 3 boosters, or CBCs (Common Booster Cores) are independent on the Delta IVH, there's not even a crossfeed. So an engine failure would certainly cause an abort, because it means a whole booster and its propellant are lost. Another reason would be asymetrical thrust. If you shut down one of the side engines, the rocket would violently spin on its yaw axis and disintegrate.
But the RS-68 have an excellent reliability record, and are really nice pieces of hi-tech.
Also note that the Delta IVH isn't, as far as I know, man-rated. The Launch Abort System was added for this test flight in order to make sure it jettisons correctly during the ascent. In fact, that test-flight is probably a good step towards man-rating for that launcher, as everything went flawlessly.
As far as I know, the first manned Orion launch will use the SLS "70 tons" (which is designed to be man-rated) for a circumlunar or lunar orbital mission profile, but we have several years before that.