The short answer is yes!
Cured tobacco leaves contain oils which contain vital flavour elements. As cigars dry out due to improper humidification, these oils are lost, and in the process the vital flavour components are ruined. A dried out cigar may be re-humidified, allowing it to burn properly, but the flavour components cannot be brought back and the cigar will taste stale.
Cigars that may have dried out over a short period are likely to be fine, but those left out of a humidor for an extended period may be too far gone. When stored correctly in a humidor (at a relative humidity around 70), cigars not only maintain their quality, but develop further adding nuance and complexity over a number of years. Under the right conditions, premium cigars may be stored indefinitely.
The ideal conditions for long-term storage may not necessarily be the best conditions for immediate smoking however. Check out our tips on how to avoid plugged cigars.