Let me see if I can understand this... you have two separate, unrelated issues/questions here:

1. Your son booked a flight on Southwest. At some point prior to the departure date, Southwest notified the son that it had changed its flight schedules such that the flight's departure time was different than originally booked. Correct? (How much of a change was it - e.g., how many hours was the new departure time from the original?).

- Typically the passenger can cancel and get a refund without a fee if the schedule change was significant and the new times don't work for the passenger. It can vary by airline, but for example a 10 minute change in time isn't significant but a couple of hours or more might be. There isn't any right to additional "compensation" in such a situation other than a refund of the ticket if appropriate, as mentioned above.

2. You're inquiring, for future reference, about VDB (neither IDB nor VDB were the issue the son experienced with a pre-departure date schedule change, as I understand it).

- The alternate flight arrangements are up to you do discuss with the gate agent in determining whether to accept their VDB offer. The very next flight may or may not be available. Don't agree if you aren't willing to live with it.

- The "initial offer" from the GA may vary depending on the airline or the individual GA...some may try to low-ball initially others may come out with a decent offer right away. Some airlines may offer a free flight voucher, others a "dollars-off" voucher, the latter seems to be more common these days IME. I've not heard of cash being offered for a VDB. My assessment of what is fair usually depends on how long the delay is until my re-assigned flight would get me to my destination. On average I've usually picked up around $400 voucher (for domestic flights).

- Remember the GA's focus is on getting the flight out on time and avoiding an IDB. In other words they're looking for the path of least resistance. Make their life easier and you may improve the odds of being selected. For example, already have researched and written down alternate flight options that would work for you; don't try to ask for odd routings or something unusual; be pleasant and understanding; while you can negotiate the VDB compensation amount, don't be unreasonable or the GA may just move on to the next volunteer who will be "easier". If you've asked to be put on the volunteer list, stick right by the gate and be ready if you're called to the podium...they won't wait long before calling the next volunteer up.