As the others have noted, this likely falls under the "it all depends" heading, so a couple of senarios:
Source for a disk-based, console video game - This would likely have little impact on the company since they tend to not make any changes to the game once it has been burned to disk. Granted they might lose some time if there is library code that they have to redevelop, it wouldn't be that bad.
Source for a downloadable video game - This would likely be bad since the the customers are likely going to expect that bugs will be patched, not being able to do so could cause the customers to lose faith in the company which could adversely effect future releases.
Source for a game in development - Most video game companies cannot afford to lose the code for a game currently in development unless it is extremely early in the development cycle (i.e. days, maybe weeks into it.) For a small company, losing the source for their flagship release could cause them to go out of business.
Source for a small business application with a limited release audience - Unlikely to cause any problems for the company, although they might lose a couple customers.
Source for a large business application with a limited release audience - Another situation where it might cause the company to go out of business due to the loss of faith from their customers. Even in most small markets there tend to be more than one company operating and this could be enough for the business to move to a competitor.
Source for a major application from a large company - Here is where it really all depends and would likely be on a very narrow, case-by-case basis. Flagship products (e.g. Microsoft Windows) generally have support contracts associated with them and not being able to support the product could lead to breach of contract lawsuits. If I had to give an estimate, I would say that most people involved in the lose of the code up to senior leadership of those people might need to be looking for new employment.
Across the board though, I would likely say that the person that lost the code would be looking for a new job (and might find it hard to find one!) and they might also be facing lawsuits from the company.