Not only is Moshe bound on a mission from G-d, but if G-d were to kill him, there would be no attempt involved. G-d controls the power of life and death. So what is really going on here?
Context is important in the Torah. And to understand what happens in Shemos 4-24, we need to look at 4-23.
19 And the LORD said unto Moses in Midian: 'Go, return into Egypt; for all the men are dead that sought thy life.'
20 And Moses took his wife and his sons, and set them upon an ass, and he returned to the land of Egypt; and Moses took the rod of God in his hand.
21 And the LORD said unto Moses: 'When thou goest back into Egypt, see that thou do before Pharaoh all the wonders which I have put in thy hand; but I will harden his heart, and he will not let the people go.
22 And thou shalt say unto Pharaoh: Thus saith the LORD: Israel is My son, My first-born.
23 And I have said unto thee: Let My son go, that he may serve Me; and thou hast refused to let him go. Behold, I will slay thy son, thy first-born.'--
24 And it came to pass on the way at the lodging-place, that the LORD met him, and sought to kill him.
25 Then Zipporah took a flint, and cut off the foreskin of her son, and cast it at his feet; and she said: 'Surely a bridegroom of blood art thou to me.'
26 So He let him alone. Then she said: 'A bridegroom of blood in regard of the circumcision.'
This translation isn't very good, but it will do. There is a narrative flow to the arrangement.
G-d tells Moshe to warn Pharaoh that if he does not allow His first-born son, the Jewish people, to go and serve Him, Pharaoh's own first-born son will be killed.
But Moshe does not actually tell Pharaoh this. At least not, apparently, until much later. And why is G-d suddenly supplementing his detailed set of instructions, once again, along the way with a message that won't be relevant until the final plague?
There is one more thing worth noting. At no point did G-d command Moshe to take his family along. Moshe appears to do this on his own initiative and then appears to send them back to his father-in-law. Since they aren't mentioned again after this, it would appear that his family was sent back after the event at the inn.
G-d's warning to Pharaoh was really also a warning to Moshe. Circumcision enters a child into the covenant with G-d. It's the outward sign of service.
Moshe had intermarried while in Midian. And he had named his first son to reflect his exile. When he took along his family to Egypt, he was also bringing his son, at least one of whom was uncircumcised. How could Moshe go to Egypt and demand that Pharaoh free the Jews to serve G-d, when at least one of his own sons had not joined the Covenant?
G-d's warning to Pharaoh could be seen as an indirect warning. When Moshe does not heed it, he receives a second more dangerous warning that his wife understands and interprets correctly.And acts.
When Zipporah calls him a bridegroom of blood, she is describing the redefinition of their marriage. The circumcision sanctifies their marriage by reframing it in Godly terms. A marriage is Godly to the extent that its participants build their lives around incorporating those values in their lives.
Like Yosef, Moshe had spent most of his life apart from the Jewish people and any of their practices. The circumcision demonstrated Zipporah's commitment to living a Jewish marriage with her husband making it their second wedding.