How will a damaged logbook affect pursuing a career as a professional pilot?
Well, you've already covered the "What to do if you've lost your logbook" bit.  The remaining bit of your question is a little trickier to answer, but not as bad as you might think.

The good part about renting is that as you've noted you can get the rental records &amp; that gives you a good start on at least the hours portion of reconstructing your logs. The Day/Night, Instrument/Simulated Instrument, and destinations (Cross-Country) times may be a bit harder to reconstruct, but with a little luck you'll be able to piece that together too.


Will you have trouble with additional ratings? No.
This is the tricky bit though: You will need logs that prove that you meet the aeronautical experience requirements for any new rating you're pursuing, so if you're working through your instrument/commercial/multi and you just washed the records of that training time, cross-country time, etc. you're going to need to either reconstruct that (from rental records &amp; landing fee receipts), fly the hours over again, or some combination of the two.
The same goes for any endorsements you have (tailwheel, high-performance, etc.) - you'll need to get re-endorsed to have a record of those (and if you show up to your next practical test in an aircraft that requires an endorsement the examiner may ask to see that endorsement).
Will you have trouble with employment? I doubt it.
Your certificates are your major qualification, and you'll have those (subject to reconstructing the requisite aeronautical experience entries like I mentioned above).
You'll want to reconstruct as much of your logs as possible because all that experience should count when you go sit down with an employer, but if you've "only" washed ~50 hours you'll make up most or all of that experience in your future training.




A few related questions you might want to look at:


What is the best way to keep logbook entries backed up?
(For my part: I scan each page once I've filled it.)
Are there any best practices for transitioning from paper logbooks to electronic logbooks?
(if you decide to go that route)