Nimbus admits to leaving the induction ceremony early; it doesn't feel right when Neomuna is still overrun and the Witness is at large.
If you ask them, a better way to honor Rohan's legacy would be to finish his unfinished business and find the Vex's copycat Veil.
Apparently, early in his training, Rohan stumbled on the Vex building what he believed was a copy of the Veil. Convinced this was a threat, he spent the rest of his career trying to retrace his steps through the Nexus. Nimbus believes Rohan succeeded right before the Shadow Legion's invasion.
They ask for your help finding Rohan's notes, hidden all around the city in encrypted data packets. To recover the data, you will need cipher qubits, which can be collected from the Vex.
Defeat Vex in Neomuna to collect qubits and recover Rohan's data packets.