Bear in mind that the flasher is simply a very low-capacity circuit breaker. When it heats up from the load of the bulbs, the breaker opens the circuit, cools down from no load, closes the circuit, and the cycle repeats.

This is what makes the lights flash.

Assuming that the wiring is correct, any of the turn signal bulbs coming on is an indication that a flasher [of unknown condition] is present. A missing flasher would cause an open circuit.

Although the lights may not flash [stay on solid] because of a bad flasher, they also won't flash if the circuit does not have enough load (e.g. not enough bulbs lit). Trace the non-working bulb issue (wiring, sockets, bulbs, grounds) before losing sleep over the flasher.