C D:
EAD renewals are usually back-to-back, so there wouldn't be any gaps provided you have applied well in advance, so even if you don't receive your renewed EAD and continue working (provided the employer doesn't notice or doesn't object) that shouldn't affect your GC or citizenship at all.
While on the topic, I'd like to warn fellow members that though EAD renewals are back-to-back, AP renewals are not, and I consider it very unfair. What I mean is that say if your EAD expires on March 31, 2003, the renewed EAD would be valid from April 1, 2003 through March 31, 2004. That's not true with AP, if your AP expires on March 31, 2003 and if you applied well in advance and received an approval say on Feb 15, 2003, your AP will be valid from Feb 15, 2003 through Feb 14, 2004.
If this is not the case with any of you'll let the forum know. At least this has been the case with me.