Hi Felix,
you don't need to deploy the process definition on each restart of your application as long as it doesn't change, deploying the process definition once is perfectly enough. The Process definition is persisted in the database and will be there after the restart so your workflow will work fine by using the already persisted version in the database. You can check if a precess definition is there by using
int count = repositoryService.createProcessDefinitionQuery().processDefinitionName(processDefinitionName).list().size();