The show continued on in the comics, and they didn't die, even Wesley & Gunn lived. If the reboot uses the lore from both comic book series, they could potentially start off from there. If the reboot uses both shows endings as a jumping off point, then they could technically go with Angel & Spike are both dead. Considering that it's been 20 yrs now and David and James are not actual unaging vampires, it'd be pretty obvious that Angel & Spike have aged. Or perhaps they could go with Angel and Spike did survive and won the Battle of LA, and both were able to become human again.

What ever way the reboot goes, I'm excited for it. In my heart if hearts, I want Buffy and Angel to end up together. They'll always be my top OTP.