(Following comments by Jia Jia on the mailing list):

To be more explicit that the retransmission rules apply to all
Query messages (not just the initial one), I would update 5.3.3. 
This could also indicate something about what values to use for
T1/T2 in this case, although I am not sure exactly what to say here.

- Same T1/T2 as for initial Query seems reasonable (these are in any
case implementation chosen)

- I don't see these as being tied to the RS-Validity time. T1/T2 are
about trading off the the reliability of packet transfer between 
particular nodes and the urgency of a particular message; the RS-Validity
time is about how likely it is for a path to change. You can imagine
scenarios where one could be much larger than the other, either way round.
So, I would leave this open.

- The question about the T1/T2 setting vs. the Timeout value from 
SendMessage is a good one. Strictly these are different concepts, since
T1/T2 apply only to Query messages, whereas the Timeout applies to 
all messages. But it seems reasonable to say that T2 SHOULD be chosen 
to be less than the Timeout requested for the message.