You will always be able to get a bus back to your car if you leave it at DAK. It doesn't matter if DAK is closed, the park to park bus runs until the MK is clear of day guests. If you stay to park closing, there will be a bus available to take you where you need to go.
When I was driving, I closed many a park or DTD, policy was always take the guest where they need to go. I will neither confirm or deny that some bus drivers had been known to drive a guest directly to their car at DAK when I was a CM. It could be different now, so don't plan on that bit of magic.
It's 50-50 whether to drive yourself or take the bus. Driving yourself could be faster but you have to factor in getting to your car at AK, driving over to the TTC, then catching the monorail or boat to the MK entrance (plus security time at the TTC) while the AK to MK park to park bus drops you at the MK bus loop. If your timing is great, the bus will be faster, if you just missed the bus at AK, driving may be faster.