After fighting my way to lowest level of the tombs in an attempt to get to Lassel, He wasn't there. I went up to spiked room and still no Lassel. Unfortunately I have no saves that will take me to before starting this quest. Any advice to keep this from breaking the game will be much appreciated.

I don't know if this makes any difference but have you staked the other 2 vampires yet? Maybe he doesn't show up in the lower level until you've done so.

I did kill and stake the other vampires before going to lower level. Unfortunately my last save before this is 40 game days ago. This will be my 3rd playthrough, and everything was going so well til this. Wish I could figure out what I did to break it.., so I can avoid it next time Im down there. Regards, Jon