How well is Drupal calendar content recognized by search engines?

I have a client who's been using an ancient (by web standards) Perl-based calendar script program (called, dully enough, "CalendarScript", which hasn't been updated in years.

I've recently converted other parts of her site over to Drupal 6.x, and have been strongly recommending moving off of this old calendar script out of both security concerns and usability reasons. However, she's used it for many years and is reluctant to abandon it.

The single biggest concern she has actually has nothing to do with the functionality or security of Drupal; it's about whether/how well search engines will recognize the content from the dozen-plus calendars filled with content that she has. The current Perl-based calendar content is picked up reasonably well by Google/Bing/Yahoo; she's worried that making the switch will negatively impact how well the content is recognized by them.

Could any provide any information about whether this is any cause for concern?

Thanks in advance!