I can understand having a wage structure, but from a financial risk point of view it would make absolute sense to offer him £20k IF he is at least tempted to stay.
1 million a year to keep one of the best players in the league, who is already here, settled, fits in with the style of play and knows the level of fitness he needs to be at? How much would it cost to replace him? Even if we get someone proven on a free, they're going to be on at least 10k, and there's the risk of multiple unknowns that they may not reach near the same levels, fit in, prepared to train as hard etc.
We could go down the same route and sign an upcoming unknown to replace him, but that's going to cost at least 500k plus minimum 5k wages, and again, unknowns of how good they'll be and would still take them a year or so to get fully up to the levels Gus is at now if by some miracle they are THAT good.
Yes, he could get badly injured, but so could his replacement on 10k or 5k or anyone in the team, the risk of injury is open to every footballer. We could spend the money on two flops like Waghorn or Kane - at least we know Gus is good enough if fit.
Furthermore, if he extends his contract for 1m per year, it's going to add at least 1m to his value anyway.
Offer him a bumper deal, with a clause that he can leave after 1 season for 5/6/7m plus if we don't get promoted, and it's literally a 500k investment (if we assume any replacement is going to be on around 10k anyway) to have a good chance of challenging for another year.
No brainer for me.