Let \( p \) be the probability that the company pays the quarterly dividend, and \( 1 - p \) be the probability that the company does not pay it. The problem gives us the following conditions:
- If the company pays the dividend, the probability that the next one will be paid is 0.7. Thus, \( p = 0.7 \).
- If the company does not pay the dividend, the probability that the next dividend will not be paid is 0.5. Hence, \( 1 - p = 0.5 \).
Now, in the long run, the total probability that the company does not pay the dividend can be calculated as follows:
\[
P(\text{no payment}) = (1 - p) \times (1 - p) + p \times (1 - 0.7) = 0.5 \times 0.5 + 0.7 \times 0.3 = 0.25 + 0.21 = 0.375.
\]
Thus, the probability that the company will not pay the quarterly dividend in the long run is \( \boxed{0.375} \).