Clearly you don't get it.
If Apache walks away from the JCP, does this mean all of Apache's Java based projects will cease to exist?
Bzzzt. Sorry wrong answer.
If Apache walks away from JCP, does this mean that Apache's Java based projects will cease to get enhanced and supported?
Yeah, you guessed it, the answer is still no, they will continue to grow and be supported.
Taking Hadoop as an example.. too many people and companies have bet their company on the code.
StumbleUpon, Yahoo!, Facebook, Cloudera, Twitter, etc ... all rely on Hadoop as a core component of their companies offerings. They all have people who are contributors to the code set. If Apache were to walk away from the JCP, will these companies toss out Hadoop? Really don't think so. Especially Cloudera who's business model is based solely around Hadoop. So the Apache projects will live on. As you so readily point out, Apache's model is based on voluntary contributions of code and its in these companies best interest to continue to voluntarily maintain the code.
Now, lets say you're right. Just for the sake of argument.
All of Apache's projects are well under Apache licenses.
Suppose Apache walks away. Oh no! What will Oracle do?
Hint: They'll pick up the code, and maintain their own in house release.
Oh and guess what. They'll re-license it as their own and it will then be proprietary, or under GPL if they so choose.
So even if you were right and Apache does walk away from everything Java, it only hurts Apache.
Oracle is calling their bluff, and IMHO it was a weak bluff and a stupid one on the part of Apache.
Maybe you should pay more attention to game theory?