A couple points from my Admin O' days...

1. Anyone can get RIF'd. The difference is if you're reserve and you resign, they have to approve it unless there is a stop loss or another technicality (like dropping your letter before/after 9-12 months out). If you are a regular officer, they can say "no" to your resignation without a reason.

2. If you are RIF'd, they have to pay severance to a regular duty officer, but not to a reserve officer since even if they're full time, they are still "temporary". If you FOS, you still get severance either way.

2a. Policy has been, since 1994 or so (the last RIF, where they looked at reserve officers exclusively), to treat regular and reserver officers the same.

3. High Year tenure for an O-4 is 18 yrs. Depending on the mood, they'll either automatically give you a waiver to get to 20 or they'll make you request a waiver. They burned a bunch of dudes a couple years ago when they changed policy to "request" from "automatic" and guys got their walking papers 2 yrs short as a reward for not watching the message traffic. So, O-4 = 20 is not a sure thing.

HTH
Spongebob