[Paul Gibbs]

For the first question, I don’t know where you are hooking your code into. Are you able to use bp_get_the_topic_permalink()?
For the second, no. You’d have to pass along that text with the page redirect in, i.e. $_GET, and then hook into an action so you can squirt the text back into reply_text textbox with Javascript.

If you submit an enhancement ticket for this on https://trac.buddypress.org/, we could add such an action in to make it easier.