Some networks do not include much or any redundancy. In this case, there is one or more single points of failure.
If one of the non-redundant devices fails, the connection to the Internet will fail as well.
Most companies that choose to invest in a redundant Trellix IPS solution also invest in redundant paths to and from their network. That is, there are numerous companies that have single points of failure, but insist on implementing Trellix IPS failover.