If the AGE of the arp entry increases does this mean the device is offline.
In this exampe the age of 10.59.33.25 is 194 Minutes and increasing.
DRWEXTRTR02#sh ip arp vrf OPTUS-SIP
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.59.33.25 194 3c61.042f.49f0 ARPA GigabitEthernet0/0/0.925
Internet 10.59.33.26 - 00be.75e7.f160 ARPA GigabitEthernet0/0/0.925
Internet 123.102.240.97 - 00be.75e7.f160 ARPA GigabitEthernet0/0/0.927
Internet 123.102.240.98 0 0090.8fa9.e886 ARPA GigabitEthernet0/0/0.927
DRWEXTRTR02#sh ip arp vrf OPTUS-SIP
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.59.33.25 197 3c61.042f.49f0 ARPA GigabitEthernet0/0/0.925
Internet 10.59.33.26 - 00be.75e7.f160 ARPA GigabitEthernet0/0/0.925
Internet 123.102.240.97 - 00be.75e7.f160 ARPA GigabitEthernet0/0/0.927
Internet 123.102.240.98 0 0090.8fa9.e886 ARPA GigabitEthernet0/0/0.927