Member services can book cash nights. (This means you're buying the entire night(s) 100% with cash.) The down side is that they cannot offer the same discounts you might be able to get through CRO. There is a 25%
DVC member discount that is often available when booking with member services, but it is limited to a certain number of rooms at each resort for any given date. It's hit or miss as to whether you'll be able to get the discount. If you can't, they charge the full rack rate for the room. Cash reservations through member services can be made at the 11-month point.
If you're just a few points shy of what you need, there is also an option to purchase one-time-use vacation points from member services. These can be mixed with your points to book a night. If you need more than a few points for your last day, though, this is probably the most expensive option. The one-time-use points are $15 each, and you're permitted to use up to 24 of them in a use year. They are treated as non-home-resort points, so they can only be used within the 7-month booking window. (Do the math to see if the one-time-use points are more expensive than purchasing the entire night on cash. You can also do a mixture of each, finishing out one night with some of your points and some one-time-use vacation points, and adding additional cash nights.)
With both of these options through member services, the cash points/nights will be part of the same reservation as your points booking. You'll have a single check-in and there will be no distinction between the points and cash portions of your stay. You'll receive all the DVC perks (well I guess there aren't many of these left now that there's free WiFi) and will be on the same maid service schedule as you would have had with a pure points booking.
If you're an annual passholder or have access to other discount booking codes, you can probably get a better rate for your cash nights through CRO. You can also take advantage of offers like free dining or 4th night free when booking with CRO. With a CRO booking, though, you'd have two entirely different unlinked reservation from your DVC reservation. You could explain the situation to the front desk at check-in, and they could possibly work with you to keep you in the same room, but there's a possibility you would need to move. In any case, you would need to do a check-out/check-in. You would receive full maid service during your cash nights booked with CRO.