: Well firstly those two things don't have to go together, in fact they can't:
: if there's no more to give, how can you get more? Secondly, that's not
: what comes to my mind when that phrase is used. Milking something, to me,
: is making something take more time than it needs to and more time than it
: should.

Not in any context I've seen the analogy used... 'milking it for all it's worth' comes to mind. Like milking a cow when it's almost dried up; pulling and pulling until the very last drop. =P
It's no longer a major stream of produce, no longer a stream of products that are highly desired and successful; it's now a lack of willingness to let it go and move on to other fresh sources of produce, putting every effort into getting the last drop.

'Milking a franchise' to me has always meant just that - it's lived its life, people have moved on, and they're trying and pushing to keep it popular and successful by cutting corners, by compromising core values, doing things that end up actually hurting the franchise more than if it were just to be left as is.

Halo is still popular, and many, many communities and fans still want to see more (ideally) because there's still loads of potential (providing skilled storytellers and developers have it in their masterful, loving hands). But Halo is far from the 'milking' stage, imo -- only because Halo isn't just about the Master Chief. If it were, then yeah it might feel like they're stretching a single storyline out past its expiry date.

But it's not... not yet at least, imo: Depending on how they treat the Chief's upcoming storyline and place in the haloverse, I might come to think that 117's arc should come to an end.
But Halo? Definitely not!