The most common things to cause the loss of spark on magneto ignition systems with 'points' are:
1) fouled spark plug (can happen in short order if mixture is too rich and/or using too much oil and other reasons)
2) loose wires from magneto to coil or elsewhere in the harness
3) kill switch wires touching frame or handlebars etc.
4) kill switch or key switch defective
5) points not opening (this is only common when the bike has set for ages, gets put back in service, then the accumulated rust on the points cam wears the points' rubbing block rapidly)
The least common things to fail are:
1)coil (coils rarely fail on magneto/points systems)
2)condenser
3)points