You both get the best mark in your school.. the only difference in your marks would be the hsc mark.. lets say the top mark in the hsc was the guy who you tied with.. who got..99/100 and you got 97/100..
your final mark will be 98/100 (Averaged: (97+99)/2).. and the other guy will get 99/100 (Averaged: (99+99)/2)
either way it wont effect you.
No.
You do not both get the top exam mark as your assessment mark but the average of the top two marks so in your example both students would get a moderated assessed mark of 98 with one then getting 99+98 and the other 97+98 as 98 is the average of 99 and 97. Both keep their own exam marks so 98 + 97 and 98 + 99 would result in final marks of 98 and 99 and thus would be separated in the final marks.
If they were to both get the highest exam mark why wouldn't schools send in all their students with 100 and thus have them all get a moderated assessment mark of the highest student.
A couple of years ago I had two students in this situation - sent in equal first. Top exam mark was 92 (actually earned by a student other than the two who came equal first) and the second mark was 87 so the two I sent in ended up with assessment marks of 90 but they did keep their own exam marks.