Realistically Poppy is pretty close to cooked - he was noticeably less effective this year in terms, although to be fair our forward line was pretty dysfunctional for a large part of the season. Given he is almost 30, if someone is willing to offer a multi year deal for him we owe it to let him decide what he wants to do.
What's happening in AFL is similar to what happened in cricket about 20 years ago - players are now able to physically play for longer (although not at peak performance). Part of the reason you had so many one club players in the 'old days' was everyone retired around 30 because they needed to support themselves - these days a lot play to 34-35 and earn enough coin to set themselves up for life.
They may not play for teams in the window, but the experience is invaluable to a team that either lacks senior players or is rebuilding. Lewis at the Demons is a great example and Poppy to GWS would be another one.