Messi have with 499 goals and 201 assists been directly involved in 700 goals in 626 games.
Ronaldo have with 533 goals and 178 assists been directly involved in 711 goals in 786 games.
Messi has played 160 games fewer than Ronaldo and yet is only 11 goals behind. BEAST.
(According to MessivsRonaldo)
In my humble opinion, I think Messi will score 800-900 goals in his career.
There are still 14-20 games left for Messi this season, and with a goal-ratio of 0.976 per game he should be able to finish the season with 54 - 61 goals. (Reminder, he was injured for 2 months.) This should take his total to 512-519 at the end of the season.
Now, could Messi reach 800 goals before he turns 35, I think so. Look at the math.
512-519 goals before next season.
29: 58 goals
30: 55 goals
31: 52 goals
32: 45 goals
33: 40 goals
34: 38 goals
=288 goals (800 in total)