It's extraordinarily hard to draw in any kind of diving gear, let alone make it stick to the specially waxed or whatever paper/parchment/canvas etc -
Trust me I've tried it! Plus it would take ages and ages
I know it doesn't actually say
it but it would take even Leonard a fair length of time to build The Boat within a week or so of Leshp surfacing (or however long that was - certainly not long enough to properly seal the thing, even if they had all the materials to hand, unless they involved wizards) so I expect he was in the dry the 1st time around as well...
Since when does Vetinari have anything much to do with the Assassins?
Downey loathes him and Vetinari seems to mostly ignore them from a point of undoubted superiority and intellect as they ignore him back as a non-graduate from a point of extreme sulking and knowing they've been bested.
He left the Guild without 'formally' qualifying under cloudy circumstamces and appears to have had no real connections with them since or indeed, since becoming Patrician, with any of the other Guilds save for annoying the bile out of them, except perhaps the Seamstresses.
I can't be bothered to look up the quote (if there is one), but I can't remember anyone, least of all Vetinari actually saying "I resign". He said something like, "I've told you we can't afford an army. Period. So sort yourselves out if you want to fight that much. I'm not doing it."
And I certainly
can't imagine Vetinari going up to Downey and saying "Hi me old mate me old buddy fancying helping me not to go to war and not inhuming anyone, thank you so very much, just out manoeuvre Rust and crew a little bit and save the city a bunch of money?" Bit too hard to inhume the entire Klatchian Army isn't it? Plus there's the question of the fee of course...
Much cheaper to let Rust go ahead and play soldiers, assuming that he's scared you off (thus 'removed' in his echoing brainpan and so martial law by default) whilst you quietly go off with Leonard, find out what the deal is with Leshp for sure and then, still in a position of being in charge (because he'd never actually relinquished that) make a seemingly disadvantageous peace treaty for which you then have to insist
on being arrested for once you're back home, knowing that you've won all along...
as though he was completely out of the picture freed him to do all he needed to do, so he looked 'removed' or as though he'd stepped down/run off, but hadn't done anything officially whislt Rust charged about to his heart's content and took all the focus off him. Manipulative enough for ya?
I don't think Vetinari's necessarily a statesman either - he's far too ruthless and nasty for that