From the first post it's unlikely that residual water is the problem. So nothing to lose by trying, but I think it's a long shot.
BTW rice is recommended as a drying agent as it's something Western homes are likely to have. Couscous is apparently better, and of course silica gel if you have it would be better yet.
The problem is, what if there is corrosion damage somewhere where you can't see it, e.g. inside the display panel rather than on the connector, inside some other component, or in some small contact on a chip on the mainboard (which may be under the chip)? A washing machine will be a pretty hostile environment (hot, very impure water for an extended period), so I'd not rule anything out. What I'm saying is that even if it's a long shot you might want to try the drying anyway, because at least that's cheap. The risk with buying a new display is that if there's a problem on the mainboard it will have been a waste of money.
The problem is how to test whether it is just the display? Maybe try booting the phone and then calling it or something, to see whether it will respond at all (i.e. whether the display is the only problem)? Unfortunately the S6 series had no MHL or USB to HDMI support, so there's no simple way to mirror the display to a TV, which would be an easy way of confirming whether the rest was working (Chromecasts are useless for this because you need to set it up, which you can't do with a blank screen - wired mirroring is just much, much more useful for diagnostics or data rescue with a dead screen, but not something Samsung regarded as a priority).
