Warnings when loading a project

When I tried to load a project today, I got these warnings:

The plug-in “HALion Sonic” could not be found for Instrument Track “TRAIN Chords”!
The plug-in “HALion Sonic” could not be found for Instrument Track “Aura Synth”!
The plug-in “HALion Sonic” could not be found for Instrument Track “ARP”!
The plug-in “HALion Sonic” could not be found for Instrument Track “ARP (D)”!
The plug-in “HALion Sonic” could not be found for Instrument Track “Strings”!
The plug-in “HALion Sonic” could not be found for Instrument Track “5th Pad”!
The plug-in “HALion Sonic” could not be found for Instrument Track “LEAD SYNTH 1”!
The plug-in “HALion Sonic” could not be found for Instrument Track “LEAD SYNTH 1 (D)”!
The plug-in “HALion Sonic” could not be found for Instrument Track “LEAD SYNTH 2”!

I think it might be because I availed of the Cubase #Stayhome Elements Collection offer https://bedroomproducersblog.com/2020/04/03/stayhome-elements-collection/#:~:text=%23StayHome%20Elements%20Collection%20is%20a,2nd%20until%20May%2015th%2C%202020. and downloaded Halion Sonic 3. If I used sounds from Halion 3 and the offer is now expired, would I get the above warnings?

If that is the case, the only way to restore my project would be to buy Halion 3, I assume?

Probably yes. Seems like your 60 days license has expired and you can no longer use Halion.