Personally, I'd reject the offer of a rebate even though its a really solid gesture on their part! Props to them, but the cost of membership (per month more so) is fairly negligible in the grand scheme of things, for me as an individual whereas it's a big number for a club that has hundreds of members or more.
I'd rather see that the grounds don't move further in the direction of the abyss than that I recoup costs of "not shooting". The way I look at it is not so much that I pay them for the opportunity to shoot each and every month, but rather that I'm a paying member of the club for whom the grounds provides all of our shooting opportunities present and future. I support my grounds wholeheartedly for it and have put extra money in last year through sponsorship and a private contribution towards new structures, and will do so again.
Essentially, there's no shooting (here anyway) if the grounds fall short of funds to stay in business. Any club that now loses its footing is unlikely to re-open post-Covid and the numbers weren't great to begin with. I imagine that cost of upkeep, maintenance and lease alone is quite substantial whether there's any shooting going on or not, so with the lost revenue I wouldn't expect or demand a refund, preferring that our shooters see (to it that) the club survive(s) lockdown.