Brown will probably retire on my rosters, or at least stay there until he's no longer producing at a high level. Letting players decline on my roster isn't something I usually do, but he's such a game changer that I'll make an exception for Brown.
As for guys like Julio/AJG/Dez, realistically we've already passed the prime sell-high window for them. Age is a huge deal in dynasty (warranted or not), and WR is so deep that owners just aren't going to pay big for WRs that are 28-29yo. If you wanted to truly play the value game, these players should have been sold 1-2 years ago. Situation played a large role in his fall, but DT was proof of this over the course of this past off-season. Having said all that, if you continually sell your studs in their prime then you're really hurting your chances of winning, so it's a bit of a catch 22.
The whole notion of cashing out on veteran WRs like Julio/Dez/AJG by trading them for picks during the off-season just strikes me as a terrible idea. Picks/youth rule in the off-season, so you'd be selling low on the players and buying high on the inflated picks. I think a much better way to go about it is waiting until the summer, after drafts are over and picks turn into players, then trying to sell your vets for a package of players and future picks. Sometimes it doesn't take long for owners to disconnect a rookie from the actual pick they used to draft the player, and it can become easier to buy that player after the draft than it would to trade for the pick prior to the draft.
Ideally though , you'd want to sell productive vets during the season. The downside to that is it sometimes means you have to forgo making a title push that year, but selling in-season gives you the chance to pounce on the best opportunity when it arises. It also gives you the opportunity to get the best return as you can take on injured/underperforming young players at a substantial discount, and you're more likely to find an owner who will be willing to forget about "value" and be willing to give a bit more to get a deal done because they're trying to win a title. In the off-season, nobody's forced to field a competitive roster or put points in their lineups, so they're much less likely to trade for a player unless the trade is on their terms and in their favor.