Running headers without CELs short term?

[KBC]

Halfway through a head gasket job and I'm installing headers at the same time. My rear O2 sensors are rust welded in place and I've stripped the flats so I need to replace the cats and O2 sensors if I want to add CELs.

How bad will it be If I drive around for a week or so with no CELs?

 

[Muadeeb]

I wouldn't worry. You'll loose a few mpg, that's all

 

[KBC]

I might not make it down the street if I lose anymore mpgs ha!
Thanks!

 

[KBC]

Finished tonight and let it run for awhile, then a trip around the block and still no check engine light. Am I going to regret ordering new rear cats and O2 sensors?
Also, all the never-seeze I put on the header blots and exhaust studs sure smokes hehe.