So this is the extent of my proposed alternate timeline after the end of the war:-
1. Charles XII enters Sweden into the early Industrial Revolution.
2. Charles's government also begins a massive assimilation program in Finland trying to incorporate Finnish culture into the Swedish one and lets say as time goes, he succeeds.
3. He introduces new military reforms and structuring to bolster the military of sweden
4. Sweden also pushes forward propaganda encouraging reproduction to try and increase the population
5. Beginning of the construction of the strongest baltic fleet
6. Construct a small amount, but strong forts in key strategic locations on the border with Russia.
7. Keep its small island colonies.
8. Possibly invest into exploration to try their luck at colonizing again.
9. Try to foster good relations with Russia to prevent future wars.
Basically in this ATL i have made Charles XII a more rational and outward thinking monarch who would have probably gained the moniker 'The Great' which he almost did get in our timeline.
1. How? Sweden has no coal. Until Britain (or maybe Belgium or France, or whomever controls Silesia or Ruhr) starts extracting coal at an industrial scale, there's not going to be enough coal to feed an industrial revolution. And before the agricultural revolution and land closure (OTL happened in Sweden in the 19th century), there's not going to be enough labour either.
2. While the language situation could certainly improve for the Finns, they have no real complaints about being part of Sweden at this time. Having the same rights to representation at the estates parliament, the same taxes, duties and legal rights (and less noble and state owned land as a percentage, and thus in essence less dues) as Swedish peasants, they are neither wishing for independence nor Russian domination at this time. OTL the Finns got very lucky about the Czar letting them keep their laws and govern themselves. It was not until the various wars and conflicts between royal and noble power in Sweden later in the 18th century that the Finns got fed up with Sweden's inability and unwillingness to defend them from Russian incursions and tendence to blunder into war with Russia with inadequate preparations, for which the Finns paid a heavy price.
3. Sweden is already one of the most militarised countries on the planet at this time, with one of the best quality armies, Sweden lacks the economic resources to do more, especially if you are giving away 10% of the state revenue (roughly 400-600 000 thaler) with Ingria and Nyen/Saint Petersburg. If the war has been going on, Sweden is also deeply in debt - Sweden ran a surplus of a 500-550 000 thaler in peace. Despite extensive looting in Poland-Lituania, by 1710, the war had costed more than 25 000 000 thaler, and the yearly deficit was 800 000-1 000 000 thaler yearly. It will take a LONG time to pay off that debt, which will reduce any investments in industry or infrastructure - especially since you just gave away basically the entire state surplus.
4. Reproduction was not a problem. Death to disease, child mortality and agricultural production along with the lack of infrastructure to move food to regions affected by bad harvests was the problem. About 1/3 of Finland's population starved to death 1695-97. The state imported 500 000 barrels of grain from Livonia, but it sat rotting in the ports since there was no way to bring them out into the countryside due to the lack of infrastructure.
5. Sweden has the strongest Baltic Fleet already. 38 ship of the line and 38 frigates 1700. Brandenburg-Prussia does not have a navy, neither does Poland-Lithuania. Thier vassal Courland had a decent-sized navy, but Sweden captured it when they overran Courland 1702. Denmark is the only challenger to Swedish naval power at this time - but while the Danish navy was larger, stronger and of better quality than the Swedish in the 17th century, it rarely ventured far north of the southern Baltic, aware that it needed to protect Denmark from any landing attempts. 1700, the Swedish navy had parity, and the Danish navy declined battle when the Swedish navy, supported by an Anglo-Dutch squadron landed parts of the Swedish army at Humlebaek. And now the Russians will build a navy and you have a potential two-front war.
6. Yes, this is a good idea. But you have just given away the only modern (although small) fort in the area - Nyen. Along with the entire yearly surplus of Sweden. From where do you get money for these fortifications?
7. What small island colonies? Sweden lost its last non-European posession, the trade fort at Cabo Corso in West Africa 1663.
8. The profitable colonies - trade forts in West Africa and the Caribbean sugar islands are all long since gobbled up and are being jelously guarded by their owners. The rest are, frankly, disease-ridden hellholes. Compare the attempt at the Scottish Panama colony, which ruined the country, killed 3/4 of the 1 200 settlers and was abandoned only 8 months into the attempts.
9. A good idea, actually. However, there's no guarantee that the Estonian and Livonian nobility will not see Russia as a potentially better overlord over the constant Swedish attempts to end serfdom and with the splendor of the Russian court at Saint Petersburg closer to them than the more austere court in Stockholm. Russian power projection ability into the Baltic and into Estonia and Livonia has after all improved siginificantly with the Russofication of Ingria and construction of Saint Petersburg, creating of the guard regiments there and fortifications.