Currently the TPMS shows the last update pressure with no indication of when that was. Sometimes this is obvious such as when you first start the bike on a morning which is not an issue. I might be missing something which is already present but I don't think loss of signal currently results in an alarm so at other times you would be unaware of an issue for quite some time.
Yesterday on the motorway I heard a loud ping, the sound a tyre makes when you run over something with the edge and it springs out. I don't know if it was me or the van next to me but I immediately changed screen to watch the pressure and saw it had not changed in a while. There was no fault but I had no way of knowing.
@Chigee the pressure indicator could be modified to somehow indicate the last update time was within the normal range with a warning if has not updated in a while perhaps green/amber/red combined with a zone for pressure rather than reading the number and remembering what it should be.