I have a 450 Watt Head 4ohm running to my 4x10 Cab. The other day I noticed a annoying buzzing noise from my top left 10" speaker. I popped the grill and the speaker cone looked fine, but it where the speaker cone meets the surround there is about 1" in length that has lost its seal between the two. A few questions....

Can I try and re-seal this? If so what kind of glue/adhesive should I use?

Probably a dumb question... but if I can't get this fixed in time can I just unhook the wires from the speaker and play through the remaining 3 speakers?

Thanks much in advance for any help!!!
Taking the speaker out, will, i assume screw with impedance of the cab, but i dont know how exactly, so im not gonna give any advice on that.

Replacing the speaker shouldn't be too difficult though.
Your speaker will probably not last forever and if you need reliability then you need to think about replacement. However, I have success fully repaired several speakers with this fault and the repairs have lasted a few years. The trick is to use a glue which will not harden as it ages. I use a latex based glue (Copydex) it comes as a white emulsion and smells of ammonia, rather like a gents toilet.

Gently clean off any dust and paint the glue thinly onto the two surfaces and hold them together until the glue is clear, at this stage I usually strengthen the joint with a little toilet tissue which I laminate on with extra layers of glue but just the extra glue will build up a layer of rubber over the join. Use only a single ply of tissue at a time and don't build it up too much or it will stiffen the repair. This technique also works well on tears in the cone in this case the repair lasts as long as the speaker.

Good luck