In Aperture you have highlight clipping. Is there highlight clipping in Photos?

No, Photos has less adjustments than Aperture.

You can reduce the highlights with the Highlights & Shadows sliders, but that is all.

Have you revealed all the adjustments in Photos's Adjustment panel? Click the blue "Add" at the top of the panel to add the adjustments you want. The advanced settings are hidden behind the disclosure triangles. And the panel is scrollable, what you might miss, if you did not set the scrollbars to show always.

You can continue to use Aperture as long as you have the current version 3.6

LN

Aperture will continue to work even with the next MacOS X version El Capitan, if we can go by the current Beta.

The next version of Photos will support photo editing app extensions to interface with external editors, have a look at the El Capitan Preview. Apple — OS X El Capitan

That will making it easier to use external editors.

New editing extensions let you go further with your photos.

OS X El Capitan supports third-party tools that will be available from the Mac App Store and accessible right in the Photos app. Use multiple editing extensions from your favorite developers on a single photo, or use a mix of extensions and the editing tools built into Photos. From adding subtle filters to using beautiful texture

I just wanted to try out Photos for family pictures and sharing as you cannot share images in Aperture anymore using web galleries.

What you can do in Aperture is using "Shared Albums". You can publish shared albums as a webpage and send the URL to your family and friends. The webpages are only accessible using the shared URL.

iCloud Photo Sharing FAQ - Apple Support

Can I share with people who don't use iCloud?

Yes. If you enable Public Website in the settings for your shared album, your photos will be published to a website that anyone can view in an up-to-date web browser.

I hope that Aperture will continue for many years as it is a great app. Much better than Lightroom in my opinion.

Me too. I have been trying out the photo application, "Lyn". It Looks like a good alternative to Aperture and iPhoto. And like Aperture, it has the ability to display Keywords under the Thumbnails.