fear/dread that someone/something "will" vs "might"

Question

This is a very academic point. The translation for "Ils redoutent qu'elle ne revienne" is given as "They dread she might come back". In French, they dread that she will return. In the given English translation, even the possibility that she will come back is a cause for dread. I know that, in common speech, the distinction might never be made, but shouldn't the equivalent sentences be as follows? "Ils redoutent qu'elle ne revienne." = "They dread she will come back." "Ils redoutent qu'elle ne puisse revenir." = "They dread she might come back."

Accepted Answer

In French, using the subjunctive casts the statement in uncertainty.
Ils redoutent qu'elle ne revienne. -- They fear that she might come back.
English does not use the subjunctive in these cases and has to resort to other means to express the uncertainty. That's why, in English, we say "might" instead of "will". In French, this is not necessary.

Answer

Bonjour Harry !
What an interesting point you raised!Let's start with building on Chris's answer: indeed, in French here, it's the Subjunctive mode that brings the notion of uncertainty to the statement, expressed in English with "might". Now, note that in French, modulating modals like "might" or "may" that quantify probablity do simply not exist, so nuances such as the one you expressed here between "will" and "might" can't really be expressed.Therefore here, the same French sentence can have several English equivalents:
Ils redoutent qu'elle ne revienne. = They dread she will come back. = They dread she might come back. = They dread she may come back. 
As for your suggestion of Ils redoutent qu'elle ne puisse revenir, the verb "pouvoir" takes on the meaning of capacity in this context, thus making the sentence equivalent to:They dread she may/might/will be able to come back. 
I hope that's helpful, and thanks again for this very interesting reflection :)
Bonne journée !