It may interest you that a virus which kills its host won't spread as well as viruses which co-exist. This is basic from epidemics transmission rate. The longer an infected host keeps spreading the infection on, the more individuals will be infected. If the host is killed it will no longer spread the infection and therefore the infection may infect fewer hosts and this reduction in transmission rate alone may prevent a major outbreak.
In nature, we usually only consider two success metrics: hosts infected and hosts killed. To maximize hosts infected, keeping the host alive and transmitting is very successful, so the most successful examples are those we barely even take note of (common cold, intestinal worms, etc.). To maximize hosts killed, in the physical world you either need a long incubation period where the host stays alive and transmitting (AIDS) or agressive transmission methods that humans have been getting quite good at shutting down (with the exception of transmission by mosquito).
In the world of digital viruses traditional metrics can apply too (Ransomware is measured by hosts "killed", botnets by hosts infected), but those are no longer the only interesting metrics. A virus that spreads within a certain IP block and one month after inception bricks everything it can reach might be regarded as highly successful, despite killing itself in the process.
https://en.wikipedia.org/wiki/Mathematical_modelling_of_infe...