We know that in 110 days, your domain will expire. We also know that the formula for earning coins is:
|(points above 45)^0.6|
(as said here)
So let's say, you hit 45 points in 10 days. We know now that in 100 days, you must hit 350 coins. So
amount_earned_in_a_day*100 = 350 -> amount_earned_in_a_day = 3.5
= x^0.6 = 3.5 = x^(3/5) -> 3.5^(5/3) = x -> x = 8.068
Conclusion: So in order to have 350 coins before your domain expires, you'll have to earn 8.068 points a day*, which ressembles roughly to 2 or 3 posts a day.
*and you need to stay above 45 points every day!