It's true that Trump appears to be the kind of person who wouldn't want to resign so easily. Besides, he might be good for the domestic economy.
But let us base our analysis on some of the forces in play. We have a background where Trump lost the popular vote but won in the electoral college. In my opinion such a close call is dangerous for the Republicans especially when the suitability of its front runner is almost beyond doubt, guilty.
Look at the charges against Trump and compare and contrast with the defence (assuming the Republican memo is it). The key defence is on Ukraine mainly. Yet Trump's charges go beyond Ukraine. It would appear that the Republicans are using a strategy that keeps them barely alive.
Moreover, there are fears that the Republicans are not well coordinated in their defence. Witness testimony casts doubt on the claimed innocence of Trump, yet the party appears not to have come with a new defence. Why? Because Trump may be bullying members to position.
But the impeachment process is dangerous for the Republican lawmakers. If the lawmakers support Trump blatantly, then they may also lose support at home. So they must show their loyalty to the constitution and 'democracy'.
Hence probably the best deal out of the impeachment is Trump plays his card as you suppose; the Republicans say, "we can protect you even from jail if you cooperate with us".
Remember, Pelosi and others in the Democratic party know that it may be difficult to unseat the President via impeachment. But they gain advantage if the public proceedings will depict the weak side of the Republicans. If Trump is acquitted they know it will be difficult for Republicans to keep a straight face. If Trump resigns, then Republicans have a chance at keeping the Presidency.
In the end, Trump is likely to see a resignation as a victory.