Did you check for spark once you got back home?
How does the compression feel?
The poorly reassembled muffler? Did the end cap come off or did it come loose at the cylinder?
Can the engine start and run at idle? And if so, does it free rev or just bog down when trying to rev the engine?
the reason for the questions is because it could be one of a few things.... it could be as simple as your head worked it's way loose and needs to be re torqued, which will cause a loss of compression bad enough to prevent it from starting, or if it does start it'll just bog down when trying to rev the engine.
If the exhaust came loose at the cylinder and you kept riding it, this could be bad because the cold air can get sucked into the exhaust port and distort the rings or even worse, melt part of the piston. Luckily, pistons and rings are cheap for these and easy to replace.
If it's not getting spark, then we need to first look at the plastic boot on the spark plug wire, these are notorious for failing, and also look at all your wiring connections, they need to be firmly connected and the terminals need to contact the wire, sometimes the culprit is a bad wire terminal that wasn't crimped down tight enough and you got a loose wire making and breaking contact, or it was crimped too tight cutting the wire so it only contacts intermittently. Check that all the contact terminals are insulated or wrapped with electrical tape etc... a bare terminal can slap against the frame shorting out the power from the mag to the cdi. Another common issue is the ground wire on the magneto, make sure it has a good contact to the metal core on the magneto, these are coated with varnish at the factory and sometimes that thin layer of varnish is enough to prevent a good ground contact, and the blue wire has been known to come un soldered from the coil which will prevent a spark.
Also, if the mag coil got wet it's gone.
Check your head nuts to be sure they didn't work loose, check for spark, then check compression if you got a compression tester, you can also check if the engine has a good resistance to turning over with the mag cover off and using a 14mm wrench to turn the engine over, it should have a decent amount of resistance then go easy as it turns over, if it turns over real easy or you can turn the mag rotor by hand without a wrench it's possible you lost compression either from a loose head nut or a scratch in the cylinder bore... cylinders are cheap too so not too much to worry about, but do all the basic checks, spark, compression, and fuel delivery, then get back with us if you don't find the problem.
Also, pictures help a LOT when troubleshooting in here