Hi William!
Well, if the people didn’t know that something was coming they do now!

I’d say that the people deserve the respect of being part of the decision. I have several good friends who are RC priests in areas where they have had to merge parishes. The process seems to be accomplished in one of two ways.
Method One is where the bishop simply merges and closes the parish with no preparation and little or no input from the people (those who are the Church). This almost always results in people getting hurt and some or many simply leaving the Church altogether.
Method Two is where the facts are put before the people and they make the decision (they are the Church and it is really their decision). In the case of a parish closure or merger I’ve seen a process taking three years where the people are given the facts. For example, the economic decline of the inner city has led people to move to the suburbs, where there are new parishes, resulting in the loss of people and the income necessary to support the parish. The people then discussed all possibilities, including evangelizing the local neighborhood to closing the parish. Sometimes when the parishioners see that they can’t make it financially (for whatever reason) they make the decision themselves to merge or close. Not everyone is always pleased, but at least if the parish is merged or closed the people knew that they were part of the decision and really explored all options.
Your question is, of course, different.
I’d suggest the possibility of simply telling the parishioners that the current schedule simply doesn’t work anymore, give the reasons why, offer some suggestions (maybe those you have listed), and then ask them for their suggestions. And then have meetings in the parish (maybe after an evening holy day service) to discuss it. Some pastors would allow a nonbinding vote on such a thing but others won’t allow even that. But an RC pastor friend of mine had a similar problem (he was pastor of 4 parishes at the time!). When he had a series of meetings over coffee and cake the parishioners made the decision for themselves that everyone understood and most supported.
It would be ideal, of course, to have plenty of clergy to support regular Vespers on Saturday night and Divine Liturgy on Sunday morning. That is just not possible at present. If you are in a parish that does one of those “Vespers and Divine Liturgy” combinations, you might consider just having a regular Divine Liturgy (without Vespers) to draw additional people. As much as I love Vespers it is just not a draw when you take half of Vespers and half of a Divine Liturgy and almost always chases people away. [That is a combination unique to a few days a year.] The truth is that Vespers needs to be Vespers and Divine Liturgy needs to be Divine Liturgy. Our liturgical services don’t make sense when recast into something they are not, and the people instinctively know that.
Prayers and best wishes to you and your parish.
Christ is Born!John