Who should be liable for the loss?
No one. Electrum doesn't come with any guarantees, and it's not like you paid for anything anyway. I would also like to note that anything before Electrum version 3.0.5 has a critical vulnerability where your seeds can be viewed remotely via malicious scripts if you don't have a wallet password, or have a weak one. That was huge news and you should have updated then.
I assume you've had this wallet for a while? Does it come with a strong password? You've either been compromised with malware or got your vulnerability exploited.