Do you know anything about the road from Uyuni west over the boarder into Chile and then San Pedro Atacama
That's a serious expedition, long gaps between food and water, and roads that are just jeep tracks worn into the land. There are several routes and they aren't well mapped, but people find their way by one route or another, there aren't many choices to be made, and the standard routes are fairly well worn by the jeep tours. You need to carry about 10-12 days food because there isn't much even in odd village you do encounter. Water management is also hard work, in general you'll get water every second day, but of course need to have some conservatism in case you get delayed by weather, weariness or whatever. Though there will be regular jeep tours going by for assistance if you get into trouble, and sometimes you can beg water off them.
Some general comments here I made on the basis of going on a landrover tour in the area.
http://www.transamazon.de/links/ivan/bolivia.html
There's a lot of material on remote routes in SW Bolivia and other parts of the Andes here which must surely cover it
http://pikesonbikes.com/
They have also written a book called "Andes by bike"
Here's another description among several "off the map" routes in the Andes
http://www.irisentoreopreis.nl/lagunaverde.shtml
There are plenty more accounts to be found, I'm sure. This guy (sporadically) keeps a catalogue of them http://www.transamazon.de/links/ though a lot of the older links are dead now.
The key decision is whether you cross the Salar or take the shorter route via Villa Alota to the south of the Salar. Crossing the salar is much the more scenic route, not just for the salar itself but for other lovely sights in the western borderlands before you get to Laguna Colorado where the routes join. But it includes some nasty soft ground and very indistinct tracks, and you can end up dragging your bike across soft ground for a few tens of km here and there. You pass the Chiguana military post and in the past cyclists found it important to beg water off them, but I have heard it might have been closed. Sol de Manana is an optional detour between the S end of L Colorada and the next lake south, for all they say about it, it's actually only about 4900m, but it is still a big steep climb from L Colorada, especially at that altitude.
Laguna Verde is of course the single most famous sight - you'll be lucky to see it in the snow as I did, as evidenced by the photo at the top of the page. But you can shorten the journey by omitting Laguna Verde and cross to Chile further north, there are 2 or 3 options, and going via El Tatio.
In general you need to check in Uyuni where active border posts are, and get stamped out in Uyuni if you are using a border without an active post.