That is -of course- a legitimate concern. However it is not perl-specific. If your system would work with PHP, the concern would be the same.
If PHP weren't as popular, the concern might be the same.
One of the questions that a serious client is going to ask themselves is, "If the vendor goes bust and I inherit the code base (because I was smart enough to write an escrow agreement into the contract), am I going to be able to find people with sufficient skill, and at a reasonable rate, to maintain and extend the product?"
That's an easier Yes if you're dealing with Java, C#, and maybe PHP and Rails.