I think Rodger's contract tells us a number of things.
1. They've got a lot of money devoted to him for the next few years, so a high pick on a QB is unlikely unless they think he's washed up (or they have a player rated real high and he drops). One down/injured year doesn't seem like enough to come to the conclusion that they need to find his replacement immediately.
2. It looks like 2021 is the first year they could reasonably cut Rodgers if his play drops off in a significant way. Post June 1st cut gives them a dead cap number of around 11m, a figure that is pretty easy to absorb for the $80m or so savings over the next 3 years. a 2022 pre June cut accomplishes the same thing. What this means is that realistically, 2021/2022 is the the earliest another QB would be expected to take over. Now, they could trade him too, but if his play drops off it's unlikely another team would take on his contract.
3. He's under contract until 2023, when he'll be 40 years old. Few QBs make it to 40, Brett Favre played until 41, Tom Brady is currently 41. These are the exceptions. That said, if the new coach can put together a decent oline and/or a system that works on quick throws, it wouldn't be a shocker to see him play out his contract, and perhaps put in another year or two. Brady has been sacked about 26/year as a starter, Rodgers 36/year. If those numbers get closer to Brady-esq numbers in the coming years, I could see 40+.
With a target for replacement as early as 2021, taking a QB high this year makes some sense. That would give the new QB 2 years to learn, and 3 years to play out a rookie contract to make sure he's really the guy before giving him a big second contract (close to ideal on both fronts). That said, I would think this is a pessimistic way to look at things, and that in all likelihood any QB taken this year would be a later round developmental QB.
As we get to the 2021 draft, I think if they haven't taken a QB early in 2019/2020, they start looking hard at that option. That said, I could see them forgo taking a QB high until it is very clear that Rodgers is done. I mean let's be real here, when Rodgers is well and truly finished, the Packers will in all likelihood suck, which means high draft picks/good chance of a top end QB for a couple years.