@kimmy I’m really sorry to hear you had this problem. We have a guide to address this Pencil2D Project File Corruption Prevention / Partial Recovery Guide
Let me say however that if you were using a previous version of pencil2d prior to 0.6.2, it may be more difficult to recover anything due to the various problems the software had in the past.
First you can try using the latest dev versions of the software to see if you can open the file properly:
Windows (7+ [x64]) : https://drive.google.com/open?id=1juDKIkv1F8fuNruGBwauA_y-7UNWibis
macOS (10.11+): https://drive.google.com/open?id=1l-Uv8LWVGHfI95dmZq2PUMOUn7s2JlpN
Linux : https://drive.google.com/open?id=1ZdDvZx_MC3yq5nMDXI0npCC0iA03l_nV
If that doesn’t work then guide addresses partial recovery methods. One of those is indeed doing what you already did. Peeking into the PCLX / ZIP file.
There was a bug that showed the file as having blank drawings when re-opened. That was fixed in 0.6.2 It’s also explained in the guide.
Try also reading on the part about the temporary folder files that are located differently in your specific OS Since the drawings are originally dumped at the beginning of the session when the file was working could still be there.
Other than what is outlined on the guide, unfortunately I have not come to know any other way to recover files that are not inside the ZIP / PCLX file or in the temp files, if the saving operation was interrupted.
The only additional thing I can ask you to do is to upload the PCLX file to a cloud service and share the link so developers can take a look at it, but again we will do the same thing as you did, and try to see inside the PCLX if there’s anything that can be salvaged.
I’m talking at a personal level now and trust me I really would like to help more, but I’ve given support to many of these cases and It’s not good to give false hopes, basically if the drawings have been deleted from the main file and your computer, it’s impossible to recover them and no matter what I say or do won’t bring them back 
I always advise people to have multiple backup copies, and to work in cuts / scenes to divide longer animation files in manageable chunks, to avoid this. To me It happened a lot in Flash, Toonboom Harmony and After effects that my files got corrupted and I lost hours of actual paid work. Pencil2D is not an exception either so I made a habit out of that, and it’s pretty common while working in studios or large gigs.
For now try to see if the guide helps you find more of your drawings. If not then you are more than welcome to curse and badmouth the software, and when that’s done you can move on to choose another one that won’t crash or corrupt your files as much. For that we have a curated list of alternatives so hopefully those programs will allow you to work much more faster and finish your work in less time 
pencil2d-software.tumblr.com/post/145767476221/when-youve-worked-all-day-on-your-animation