I can’t tell you what Ukraine would have done if Moldova attacked, but my guess is that it wouldn’t have been anywhere close to what Israel is doing. First of all, Moldova is part of the Partnership for Peace, as is Ukraine. Both Moldova and Ukraine are also aspiring EU members. They already have a negotiation and diplomatic framework in which to operate without resorting to violence. There have, as far as I know, not been any modern conflicts between Ukraine and Moldova, so there aren’t ethnonationalist or racist tensions that affect how logically this can be approached. Neither Ukraine nor Moldova claim irrelevant religious or indigenous priority over land; there is no historical violation of human rights that led to more violations of human rights. There is no international favoritism that makes one nation significantly more powerful and less accountable than the other.

The question of how Ukraine would respond would be rely on what Moldova’s goals were - when civilians are at high risk, steps are usually taken to solve problems with less violence. For example, when US citizens were held hostage in Iran (due to the US overthrowing a democratically-elected government to install a Shah who would sell cheap oil to the US), the US didn’t just bomb Tehran to the ground (which Israel absolutely has done to Gaza), dooming the hostages to a very high risk of injury and death. When the US found out Bin Laden was in Pakistan, it sent in a tactical team instead of using a two-ton bomb.

Israel also has a diplomatic framework to negotiate, in that it and the US have established Qatar as neutral ground. Qatar has experience in these types of negotiations. Israel, with Netanyahu and other far-right officials, have consistently stated that they are not going to accept any peace treaty that would indefinitely prevent them from continuing their ethnic cleansing (all you have to do is listen to what they have said in Hebrew, and more recently, English). Israel is not engaging in normal foreign policy here. The limits that exist on other countries (diplomatic, political, and monetary) just do not apply to Israel, as has been testified by numerous international aid organizations and people who have resigned from the US State Department due to this conflict. The US provides cover for Israel and funds over 1/3 of its military, as well as providing the missiles Israel uses for the iron dome and to attack Iran.

Honestly, though, you’re asking for hypotheticals specifically because Israel’s situation just does not exist for other European countries, and that is not an accident of circumstance. Europe was engaged in war for a majority of its existence, and only since WWII has peace been any kind of priority. That takes work and compromise and recognition of shared humanity and rights. Israel has not been motivated to make the same sacrifices because it is backed by the US, UK, France, Germany, and other powerful countries. It has not been held accountable for atrocities committed during its founding, nor has anyone high up in government or the military faced any real consequences. They have been able to maintain the myth that mistakes happen, but they seem to happen with alarming regularity for Israel (and the US, but that is another discussion).