The 500 / Current Panda (but with the 1.2) is slow, but not dangerously so. I mean, if you're used to driving even a slightly bigger car with a 1.6+ engine (petrol or diesel, turbo'd) then yes, if you try to join roads, pull out etc fast, you'll be sorely disappointed and potentially risking your life! But that's a driver error to not understand their cars comfort zone or stick within it. I don't think owners of these cars are seeking high speed or fast cornering, but of course, Abarth exists for those who want handling, power without giving up style or re-mortgaging the house. Abarth, as you reference, not so good on fuel, especially for such little cars but this is Fiat's default formula of 'engine isn't broke, don't fix it', then you look across at Peugeot... Vauxhall... Ford and VW who, in the same time, produced A & B segment cars with more modern engines than the FIRE 1.2 with all sorts of issues, plus being slow, and never really keeping them (or the cars they are put in) around long enough to get them reliable.
Now, the 1.0 (is it 0.9? Thought 1.0) current engine... I have not driven. Personally I'd prefer a 1.2 but now that we're a few years past the 1.2's last year on sale, anybody buying a new or nearly new 500 / Panda (of the outgoing models) now definitely has a tough decision to make.
From my understanding, it's not really a Hybrid system like Toyota / Hyundai use. It's a 'mild hybrid' so it's got a very (useless?) alternator like boost. This is not because Fiat wanted to try and change the world with its version of a Hybrid, but rather to comply with EU laws. You know, 'so many of your sales by 20XX must be 'electrified'', and 'by the year 2050... 2035... 2030... nope, 2035... nope 2030... only new EV / Hybrid sales' laws.
Fiat can built some amazing engines at all levels of the spectrum, and the Italians in general are unmatched be it a little Fiat 500, a LaFerrari or some of the ships they build, they know their engineering and they tend to stick to older, proven, 'still works' techniques. Arguably, that's all that makes some of the legendary reliable Toyota's special, the fact that they don't reinvent the wheel every 5 years like most European brands do, right down to switch gear inside the car so that it makes for more favourable car reviews and test drive demos.. They only seem to pull out the R&D when they must.
Around 2010, the TwinAir... mixed bag, some avoided it like the plague, some had a terrible experience, others on this forum currently approaching 150k miles and counting on them. Tiny little two cylinder, big turbo. The trend of the 2010s (outside of diesel, prior to 2015 and the VW scandal). Why? EU laws on emissions getting too strict, too fast. Silly solutions like this led to these tiny engines and big turbos from all the car makers - total waste as now all that R&D went to nothing. Arguably, all the work on DPFs on the diesel front - also all for nothing now, but brought about by the same EU laws.
Blame the emissions laws for this new need for Hybrids. Over-regulation, whilst made with the best of intentions, often hinders innovation and real breakthroughs by specifying narrow hoops manufacturers must comply with. And it's not like there's any real, significant eco bonus to the mild hybrid, but for owners, as you've found, it seems like there is an everyday penalty for owners who are finding it hard to live with.
Now, as for advice....
Is the warranty / MOT plan transferrable? Make a call and find out. If so, selling point to mention when selling it on.
If not... can you not sell it privately, and agree with the owner you'll meet up and take the car to its MOT / service saving them the cash - but you charge accordingly in your selling price. The right buyer might appreciate that even just to keep the dealer service history?
Otherwise.. perhaps weigh up.. how much of what you paid for that extra is 'unspent'? Is the depreciation loss of holding on to the car another year more than the loss of not getting your service / MOT?
Also... maybe the garage would agree, to keep your custom, that if you buy / source your next 500 / Abarth via them, you can get the remaining service / MOT on that Fiat / Abarth instead?
Worth a shot. If they say no... ring up or go in and ask somebody else. One salesman / workshop person's targets might be met for the month, another's might not.. maybe a senior person will pull the strings to make it work. I've found persistence to be effective in dealerships. Been buying my Toyota oil / filter at my local dealer for two years now... ~£150 ish ... just the other week, emailed and asked the current price.. same. Sent the the link to a specialist online selling for £100 + £17 delivery to NI... dealer agreed to do £120, same day pick up... shocked but happy I chanced my arm. You'd be surprised!
I really want to drive the 1.0 Panda now... to see if I agree!
Keep us updated on what you do.