Do you think Charles made right decision to return to France ? what would you have suggested him to do ?

I wold have told Charles to stay in England and work for the cause from there. I would not have advised him to return to a country where his presence alone assured him death.

If I remember correctly, Charles does detest the idea of coming to France, for a brief moment. And I too would have advised the same to Charles.

Source: Book the second, Chapter 1, "In secret"... And I quote:

"...that perils had thickened about him fast, and might thicken faster, and faster yet, he of course knew now. He could not but admit to himself that he might have not made this journey, if he could have foreseen the events of a few days..."

Charles would have even sent his duplicate Sydney carton and rest of answer is same