My response was ECL -ocentric.
I don't think any LA Buyoff and CR interactions, have even been queried before.
I don't have any idea how exactly
that would be handled, but it looks rather straightforward.
It's a dm ruling to say it works just like regular PCs, but I can't imagine it working any different.
Lich generally advances by character class.
But 4 undead racial hit dice would be quite tasty. (which a dm can just fiat to be OK)
Wizard 16+1 is +1 CR
Wizard 17 + 4 Urhd is +1 CR too.
That would get a pile of hp, an Improved Turn Resistance feat and the mandatory Epic Spells feat going.
With the 1/2 Dragon bought off, it'd be the same
CR, but obviously more dangerous.