Yes you can have multiple marketing servers and even multiple dbs that can be mirrored and configured with a failover cluster configuration in case one goes down the other is up, you can add a Load balancer as well, in the case of a full on premise setup you can also add x number of frontal servers that perform the tracking and redirection.
https://experienceleague.adobe.com/docs/campaign-classic/using/installing-campaign-classic/architecture-and-hosting-models/hosting-models-lp/hosting-models.html?lang=en
Here is an example to give you an idea for a full on premise deployment

Here is an example of hybrid (deliveries by Adobe, MKT on premise)

Here is a hybrid deployment example for AWS
