Yeah, interrupting the channel consumes the charge. If someone stuns you while you think you're safe channeling it - it's gone.
And, hypothetically, let's say Herald was summonable in base while dead - enemy teammates get an alert saying the Herald's up and (implying the Herald knew which lane you wanted to send it), everyone in the rough area on the enemy team moves to intercept it, killing it either in-between turrets, or in the middle of the lane.
Unless your teammates move to escort it as well, but that would take pressure off of a lot of areas in the map, making it more trouble than it might be worth.