Reliable WR's are replaceable, but top tier/elite/megastar WR's not so much. Especially if a QB and WR are on the same page and have that unique understanding amongst each other. Just like how Peyton and Marvin were. You saw that evident of Monday night when Jammer picked off the pass and scored his touchdown. Complete miscommunication by the WR, and plenty of people (including some on this message board) were saying, "That wouldn't happen if that was Marvin."
It remains though however, that a lot of people have a misconception about the importance about the "other" half of the WR-QB duo, even til today. Well maybe not a misconception, but although it's hard to quantify most people will give the QB 75% or greater of the credit while the WR gets 25% or less. Now in the grand scheme of the offense I don't think it's 50-50 because the QB, if he's good, will hit other targets when his go-to-guy is covered. Which you can even attribute some of the credit going to the WR for maybe drawing a double team. A good WR will draw the double team, a good QB will realize that and go elsewhere.
All of that being said, a great WR will do all of the above, and inflate a QB's #'s. You can say o-line all you want, but let's take a QB who has had an outstanding o-line nearly all of his career. Tom Brady is an NFL legend, one of the best QB's to ever play this game in my opinion.
But, he is not a 50 TD per season QB without Randy Moss. Not even close to be honest. Just to be fair, the same can be said for Peyton with Reggie and Marvin. As a comparison however, compare Tom Brady's 50 TD passes to Dan Marino's 48, just to see how much more credit Randy Moss really deserved.
vs
Now VJ is not as good as Randy Moss, not even in the same tier. But that's a special tier that I'll put maybe 3 others of all-time in (Jerry Rice, Calvin Johnson and Larry Fitzgerald). VJ is right below that. The only WR's right now that can replace VJ are Andre Johnson, Roddy White, Julio Jones and A.J Green. These are the ones that can be placed on any team and dominate.
The true elite WR's one step above them are the ones I consider outright unstoppable. Fitzgerald and Megatron fit that category and also can replace VJ. They can still be shutdown, by the whole team, or that rare special corner.
The other WR's like Brandon Marshall, Santonio Holmes, Hakeem Nicks, etc. are good, but I think they are the types that need to be on the same page as the QB and fit the scheme most times.
Considering all of that we did mess up by releasing VJ, for this team, as of right now. Is this team doomed? No, but it's still another hill they must climb that they dug for themselves. They've tried to address it by getting the players mentioned, but with this QB and this scheme, and this o-line, we don't have the weapons that can do what they did in the past and that was due to what VJ brought to the table.