Lamela is our highest paid midfielder and his deal runs through June 2020. He hasn't received a new deal because only Lloris, Jan, Kane, and Son are on higher wages - and only just. Most of our players have received new deals because they were extended for contract length (leverage) sake or to bring their wages up in steps equal to their production.
Lamela got all of that on the front end with a 7 year £4M+ per year salary the day he signed. There's simply not reason to do a new deal for him, there's no way Levy would sanction making Lamela our highest earner while he struggled for fitness.
TL;DR - You don't have a fucking clue what you're on about.
There's no way he earns more than Eriksen, though it's pretty clear it was a bad deal all around when we signed him. It's a five year contract, with the option of an extra year I believe. So his contract runs out in the Summer unless we activate the clause. He hasn't actually been available to buy in the last two windows because he wasn't fit. This window may have come too soon to convince potential buyers to shell out for him but I guarantee he'll be on his way in the Summer. We'll see in the rest of this season, he won't be a major part of it, that's if he stays. As I've said, if we make a major attacking signing, he'll be the one to make way.