If they become relevant, then your attacker is really quite close to the device. In most scenarios, once the attacker is that close you are probably fucked anyway. There are exceptions of-course. Using in-memory encryption, ingress detection, etc you might be able to remain safe in these cases. Moreover an attacker might be able to do power-analysis without leaving a trace. Whereas pulling out the RAM-sticks after freezing them leaves more of a mark.

However, few of the scenarios involving good reason to use homomorphic encryption really stand up to an attacker having physical access to the encrypting device. Most of these scenarios are about secure shared computation. Where the threat model revolves around 'what if my computational partner is evil', not 'what if Ethan Hunt breaks in'. Generally, if someone has access to the machine, they will have access to the raw data anyway.